Display device, display module, electronic device, and method for manufacturing display device

ABSTRACT

A display device with high visibility regardless of the ambient brightness is manufactured at low cost. A method for manufacturing a display device that includes a first display element, a second display element, and an insulating layer is provided. 
     The first display element includes a first pixel electrode that reflects visible light, a liquid crystal layer, and a first common electrode that transmits visible light. The second display element includes a second pixel electrode that transmits visible light, a light-emitting layer, and a second common electrode that reflects visible light. The first common electrode is formed over a first substrate. A separation layer that reflects visible light is formed over a formation substrate, the insulating layer is formed over the separation layer, and the second display element is formed over the insulating layer. The formation substrate and a second substrate are bonded to each other with an adhesive. Then, the formation substrate and the separation layer are separated from each other. The exposed separation layer is processed into the first pixel electrode. The liquid crystal layer is positioned between the first common electrode and the first pixel electrode and the first substrate and the second substrate are bonded to each other with an adhesive to form the first display element.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a display device, adisplay module, an electronic device, and a manufacturing method of adisplay device.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention include a semiconductor device, a displaydevice, a light-emitting device, a power storage device, a memorydevice, an electronic device, a lighting device, an input device (suchas a touch sensor), an input/output device (such as a touch panel), adriving method thereof, and a manufacturing method thereof.

2. Description of the Related Art

Recent display devices have been expected to be applied to a variety ofuses. Light-emitting devices including light-emitting elements, liquidcrystal display devices including liquid crystal elements, and the likehave been developed as display devices.

Patent Document 1, for example, discloses a flexible light-emittingdevice to which an organic electroluminescent (EL) element is applied.

Patent Document 2 discloses a transflective liquid crystal displaydevice having a region reflecting visible light and a regiontransmitting visible light. The transflective liquid crystal displaydevice can be used as a reflective liquid crystal display device in anenvironment where sufficient external light can be obtained and as atransmissive liquid crystal display device in an environment wheresufficient external light cannot be obtained.

REFERENCE Patent Documents

[Patent Document 1] Japanese Published Patent Application No.2014-197522

[Patent Document 2] Japanese Published Patent Application No.2011-191750

SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide adisplay device with low power consumption. Another object of oneembodiment of the present invention is to provide a display device withhigh visibility regardless of the ambient brightness. Another object ofone embodiment of the present invention is to provide an all-weatherdisplay device. Another object of one embodiment of the presentinvention is to provide a display device with high convenience. Anotherobject of one embodiment of the present invention is to reduce thethickness or weight of a display device. Another object of oneembodiment of the present invention is to provide a novel displaydevice, a novel input/output device, a novel electronic device, or thelike.

Another object of one embodiment of the present invention is to providea method for manufacturing a novel display device. Another object of oneembodiment of the present invention is to provide a method formanufacturing a display device with a simplified manufacturing process.Another object of one embodiment of the present invention is to providea method for manufacturing a display device with high mass productivityat low cost.

Note that the descriptions of these objects do not preclude theexistence of other objects. One embodiment of the present invention doesnot necessarily achieve all the objects. Other objects can be derivedfrom the description of the specification, the drawings, and the claims.

A display device of one embodiment of the present invention includes afirst display element, a second display element, and an insulatinglayer. The first display element includes a first pixel electrodeconfigured to reflect visible light and a liquid crystal layer. Thesecond display element is configured to emit visible light. The seconddisplay element includes a second pixel electrode and a commonelectrode. The first pixel electrode is positioned on an opposite sideof the insulating layer from the second pixel electrode. The liquidcrystal layer is positioned on an opposite side of the first pixelelectrode from the insulating layer. The common electrode is positionedon an opposite side of the second pixel electrode from the insulatinglayer. The liquid crystal layer includes a first region overlapping withthe first pixel electrode and a second region overlapping with thesecond display element. A thickness of the liquid crystal layer in thefirst region is smaller than a thickness of the liquid crystal layer inthe second region. The display device preferably includes a firsttransistor and a second transistor. The first transistor is configuredto control driving of the first display element. The second transistoris configured to control driving of the second display element. Theinsulating layer includes a portion serving as a gate insulating layerof the first transistor and a portion serving as a gate insulating layerof the second transistor.

A display device of one embodiment of the present invention includes afirst display element, a second display element, a first insulatinglayer, a second insulating layer, a first transistor, and a secondtransistor. The first transistor is configured to control driving of thefirst display element. The second transistor is configured to controldriving of the second display element. The first display elementincludes a first pixel electrode configured to reflect visible light anda liquid crystal layer. The second display element is configured to emitvisible light. The second display element includes a second pixelelectrode and a common electrode. The first transistor and the secondtransistor are positioned between the first insulating layer and thesecond insulating layer. The first transistor is electrically connectedto the first pixel electrode through an opening in the first insulatinglayer. The second transistor is electrically connected to the secondpixel electrode through an opening in the second insulating layer. Theliquid crystal layer is positioned on an opposite side of the firstpixel electrode from the first insulating layer. The common electrode ispositioned on an opposite side of the second pixel electrode from thesecond insulating layer. The liquid crystal layer includes a firstregion overlapping with the first pixel electrode and a second regionoverlapping with the second display element. A thickness of the liquidcrystal layer in the first region is smaller than a thickness of theliquid crystal layer in the second region.

One or both of the first transistor and the second transistor preferablyinclude an oxide semiconductor in a channel formation region.

The first pixel electrode may include an opening portion. The seconddisplay element includes a region overlapping with the opening portion.The second display element is configured to emit visible light towardthe opening portion.

One embodiment of the present invention is a display module includingany of the above display devices and a circuit board such as a flexibleprinted circuit (FPC).

One embodiment of the present invention is an electronic deviceincluding the above display module and at least one of an antenna, abattery, a housing, a camera, a speaker, a microphone, and an operationbutton.

One embodiment of the present invention is a method for manufacturing adisplay device including a first display element, a second displayelement, and an insulating layer. The first display element includes afirst pixel electrode configured to reflect visible light, a liquidcrystal layer, and a first common electrode configured to transmitvisible light. The second display element includes a second pixelelectrode configured to transmit visible light, a light-emitting layer,and a second common electrode configured to reflect visible light. Thefirst common electrode is formed over a first substrate, a separationlayer configured to reflect visible light is formed over a formationsubstrate, and the insulating layer is formed over the separation layer.The second pixel electrode, the light-emitting layer, and the secondcommon electrode are formed in this order over the insulating layer toform the second display element. The formation substrate and a secondsubstrate are bonded to each other with an adhesive. The formationsubstrate and the separation layer are separated from each other. Theexposed separation layer is processed into the first pixel electrode.The liquid crystal layer is positioned between the first commonelectrode and the first pixel electrode, and the first substrate and thesecond substrate are bonded to each other with an adhesive to form thefirst display element.

In the above method for manufacturing a display device, the separationlayer may be processed into the first pixel electrode having an openingin a region overlapping with the second display element.

In the above method for manufacturing a display device, the adhesiveused for bonding the first substrate and the second substrate to eachother preferably contains a conductive particle. The separation layermay be processed into the first pixel electrode and a conductive layer.The first common electrode and the conductive layer may be electricallyconnected to each other via the conductive particle when the firstsubstrate and the second substrate are bonded to each other.

One embodiment of the present invention is a method for manufacturing adisplay device including a first display element, a second displayelement, and an insulating layer. The first display element includes afirst pixel electrode configured to reflect visible light, a liquidcrystal layer, and a first common electrode configured to transmitvisible light. The second display element includes a second pixelelectrode configured to transmit visible light, a light-emitting layer,and a second common electrode configured to reflect visible light. Thefirst common electrode is formed over a first substrate, a separationlayer is formed over a formation substrate, the first pixel electrode isformed over the separation layer, and the insulating layer is formedover the first pixel electrode. The second pixel electrode, thelight-emitting layer, and the second common electrode are formed in thisorder over the insulating layer to form the second display element. Theformation substrate and a second substrate are bonded to each other withan adhesive. The formation substrate and the separation layer areseparated from each other. The exposed separation layer is removed sothat the insulating layer and the first pixel electrode are exposed. Theliquid crystal layer is positioned between the first common electrodeand the first pixel electrode, and the first substrate and the secondsubstrate are bonded to each other with an adhesive to form the firstdisplay element.

In the above method for manufacturing a display device, after the firstpixel electrode is formed, an opening may be provided in the first pixelelectrode and the second display element may be formed in a regionoverlapping with the opening.

In the above method for manufacturing a display device, the adhesiveused for bonding the first substrate and the second substrate to eachother preferably contains a conductive particle. A conductive film maybe processed into the first pixel electrode and a conductive layer. Thefirst common electrode and the conductive layer may be electricallyconnected to each other via the conductive particle when the firstsubstrate and the second substrate are bonded to each other.

In any of the above methods for manufacturing a display device, a nickelfilm may be formed as the separation layer in contact with the formationsubstrate. The maximum temperature applied to the separation layer in aperiod from forming the separation layer until separating the formationsubstrate and the separation layer from each other is preferably higherthan 150° C. and lower than 450° C.

In any of the above methods for manufacturing a display device, a firstinsulating layer containing nitrogen and silicon may be formed over theformation substrate, a second insulating layer containing oxygen andsilicon may be formed over the first insulating layer, a thirdinsulating layer containing oxygen, fluorine, and silicon may be formedover the second insulating layer, and a titanium film may be formed asthe separation layer over the third insulating layer.

According to one embodiment of the present invention, a display devicewith low power consumption can be provided. According to one embodimentof the present invention, a display device with high visibilityregardless of the ambient brightness can be provided. According to oneembodiment of the present invention, an all-weather display device canbe provided. According to one embodiment of the present invention, adisplay device with high convenience can be provided. According to oneembodiment of the present invention, the thickness or weight of adisplay device can be reduced. According to one embodiment of thepresent invention, a novel display device, a novel input/output device,a novel electronic device, or the like can be provided.

According to one embodiment of the present invention, a method formanufacturing a novel display device can be provided. According to oneembodiment of the present invention, a method for manufacturing adisplay device with a simplified manufacturing process can be provided.According to one embodiment of the present invention, a method formanufacturing a display device with high mass productivity at low costcan be provided.

Note that the descriptions of these effects do not preclude theexistence of other effects. One embodiment of the present invention doesnot necessarily have all the effects. Other effects can be derived fromthe description of the specification, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an example of a displaydevice.

FIG. 2 is a cross-sectional view illustrating an example of a displaydevice.

FIG. 3 is a cross-sectional view illustrating an example of a displaydevice.

FIGS. 4A and 4B are cross-sectional views each illustrating an exampleof a display device.

FIGS. 5A, 5B1, 5B2, and 5C are cross-sectional views illustrating anexample of a manufacturing method of a display device.

FIGS. 6A to 6C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 7A to 7C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 8A and 8B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 9A, 9B, 9C1, and 9C2 are cross-sectional views each illustratingan example of a manufacturing method of a display device.

FIGS. 10A and 10B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 11A and 11B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 12A and 12B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 13A and 13B are cross-sectional views each illustrating an exampleof a manufacturing method of a display device.

FIGS. 14A to 14E are cross-sectional views illustrating examples oftransistors.

FIG. 15A illustrates an example of a display device, and FIGS. 15B1,15B2, 15B3, and 15B4 each illustrate an example of a pixel.

FIG. 16 is a circuit diagram illustrating an example of a pixel circuitin a display device.

FIG. 17A is a circuit diagram illustrating an example of a pixel circuitin a display device, and FIG. 17B is a diagram illustrating an exampleof a pixel.

FIG. 18 illustrates an example of a display module.

FIGS. 19A to 19D illustrate examples of electronic devices.

FIGS. 20A to 20E illustrate examples of electronic devices.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the following description,and it is easily understood by those skilled in the art that variouschanges and modifications can be made without departing from the spiritand scope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the description of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. Further, the same hatching pattern is appliedto portions having similar functions, and the portions are not denotedby reference numerals in some cases.

The position, size, range, or the like of each structure illustrated indrawings is not accurately represented in some cases for easyunderstanding. Therefore, the disclosed invention is not necessarilylimited to the position, size, range, or the like disclosed in thedrawings.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film,” andthe term “insulating film” can be changed into the term “insulatinglayer.”

In this specification and the like, a metal oxide means an oxide ofmetal in a broad sense. Metal oxides are classified into an oxideinsulator, an oxide conductor (including a transparent oxide conductor),an oxide semiconductor (also simply referred to as an OS), and the like.For example, a metal oxide used in a semiconductor layer of a transistoris called an oxide semiconductor in some cases. In other words, an OSFET is a transistor including a metal oxide or an oxide semiconductor.

In this specification and the like, a metal oxide including nitrogen isalso called a metal oxide in some cases. Moreover, a metal oxideincluding nitrogen may be called a metal oxynitride.

In this specification and the like, “c-axis aligned crystal (CAAC)” or“cloud-aligned composite (CAC)” might be stated. CAAC refers to anexample of a crystal structure, and CAC refers to an example of afunction or a material composition.

An example of a crystal structure of an oxide semiconductor or a metaloxide is described. Note that an oxide semiconductor deposited by asputtering method using an In—Ga—Zn oxide target (In:Ga:Zn=4:2:4.1 in anatomic ratio) is described below as an example. An oxide semiconductorformed by a sputtering method using the above-mentioned target at asubstrate temperature of higher than or equal to 100° C. and lower thanor equal to 130° C. is referred to as sIGZO, and an oxide semiconductorformed by a sputtering method using the above-mentioned target with thesubstrate temperature set at room temperature (R.T.) is referred to astIGZO. For example, sIGZO has one or both crystal structures of nanocrystal (nc) and CAAC. Furthermore, tIGZO has a crystal structure of nc.Note that room temperature (R.T.) herein also refers to a temperature ofthe time when a substrate is not heated intentionally.

In this specification and the like, CAC-OS or CAC-metal oxide has afunction of a conductor in a part of the material and has a function ofa dielectric (or insulator) in another part of the material; as a whole,CAC-OS or CAC-metal oxide has a function of a semiconductor. In the casewhere CAC-OS or CAC-metal oxide is used in a semiconductor layer of atransistor, the conductor has a function of letting electrons (or holes)serving as carriers flow, and the dielectric has a function of notletting electrons serving as carriers flow. By the complementary actionof the function as a conductor and the function as a dielectric, CAC-OSor CAC-metal oxide can have a switching function (on/off function). Inthe CAC-OS or CAC-metal oxide, separation of the functions can maximizeeach function.

In this specification and the like, CAC-OS or CAC-metal oxide includesconductor regions and dielectric regions. The conductor regions have theabove-described function of the conductor, and the dielectric regionshave the above-described function of the dielectric. In some cases, theconductor regions and the dielectric regions in the material areseparated at the nanoparticle level. In some cases, the conductorregions and the dielectric regions are unevenly distributed in thematerial. When observed, the conductor regions are coupled in acloud-like manner with their boundaries blurred, in some cases.

In other words, CAC-OS or CAC-metal oxide can be called a matrixcomposite or a metal matrix composite.

Furthermore, in the CAC-OS or CAC-metal oxide, the conductor regions andthe dielectric regions each have a size of more than or equal to 0.5 nmand less than or equal to 10 nm, preferably more than or equal to 0.5 nmand less than or equal to 3 nm and are dispersed in the material, insome cases.

Embodiment 1

In this embodiment, a display device of one embodiment of the presentinvention and a method for manufacturing the display device will bedescribed with reference to drawings.

The display device of this embodiment includes a first display elementreflecting visible light and a second display element emitting visiblelight.

The display device of this embodiment has a function of displaying animage using one or both of light reflected by the first display elementand light emitted from the second display element.

As the first display element, an element which displays an image byreflecting external light can be used. Such an element does not includea light source (or does not require an artificial light source); thus,power consumed in displaying an image can be significantly reduced.

As a typical example of the first display element, a reflective liquidcrystal element can be given. As the first display element, an elementusing a microcapsule method, an electrophoretic method, anelectrowetting method, an Electronic Liquid Powder (registeredtrademark) method, or the like can also be used, other than MicroElectro Mechanical Systems (MEMS) shutter element or an opticalinterference type MEMS element.

As the second display element, a light-emitting element is preferablyused. Since the luminance and the chromaticity of light emitted from thelight-emitting element are not affected by external light, a clear imagethat has high color reproducibility (wide color gamut) and a highcontrast can be displayed.

As the second display element, a self-luminous light-emitting elementsuch as an organic light-emitting diode (OLED), a light-emitting diode(LED), a quantum-dot light-emitting diode (QLED), or a semiconductorlaser can be used.

The display device of this embodiment has a first mode in which an imageis displayed using only the first display element, a second mode inwhich an image is displayed using only the second display element, and athird mode in which an image is displayed using both the first displayelement and the second display element. The display device of thisembodiment can be switched between these modes automatically ormanually.

In the first mode, an image is displayed using the first display elementand external light. Because a light source is unnecessary in the firstmode, power consumed in this mode is extremely low. When sufficientexternal light enters the display device (e.g., in a brightenvironment), for example, an image can be displayed by using lightreflected by the first display element. The first mode is effective inthe case where external light is white light or light near white lightand is sufficiently strong, for example. The first mode is suitably usedfor displaying text. Furthermore, the first mode enables eye-friendlydisplay owing to the use of reflected external light, which leads to aneffect of easing eyestrain.

In the second mode, an image is displayed using light emitted from thesecond display element. Thus, an extremely vivid image (with highcontrast and excellent color reproducibility) can be displayedregardless of the illuminance and the chromaticity of external light.The second mode is effective in the case of extremely low illuminance,such as in a night environment or in a dark room, for example. When abright image is displayed in a dark environment, a user may feel thatthe image is too bright. To prevent this, an image with reducedluminance is preferably displayed in the second mode. In that case,glare can be reduced, and power consumption can also be reduced. Thesecond mode is suitably used for displaying a vivid (still and moving)image or the like.

In the third mode, an image is displayed using both light reflected bythe first display element and light emitted from the second displayelement. An image displayed in the third mode can be more vivid than animage displayed in the first mode while power consumption can be lowerthan that in the second mode. The third mode is effective in the casewhere the illuminance is relatively low or in the case where thechromaticity of external light is not white, for example, in anenvironment under indoor illumination or in the morning or evening.

With such a structure, an all-weather display device or a highlyconvenient display device with high visibility regardless of the ambientbrightness can be fabricated.

The display device of this embodiment includes a plurality of firstpixels including first display elements and a plurality of second pixelsincluding second display elements. The first pixels and the secondpixels are preferably arranged in matrices.

Each of the first pixels and the second pixels can include one or moresub-pixels. For example, each pixel can include one sub-pixel (e.g., awhite (W) sub-pixel), three sub-pixels (e.g., red (R), green (G), andblue (B) sub-pixels, or yellow (Y), cyan (C), and magenta (M)sub-pixels), or four sub-pixels (e.g., red (R), green (G), blue (B), andwhite (W) sub-pixels, or red (R), green (G), blue (B), and yellow (Y)sub-pixels).

The display device of this embodiment can display a full-color imageusing either the first pixels or the second pixels. Alternatively, thedisplay device of this embodiment can display a black-and-white image ora grayscale image using the first pixels and can display a full-colorimage using the second pixels. The first pixels that can be used fordisplaying a black-and-white image or a grayscale image are suitable fordisplaying information that need not be displayed in color such as textinformation.

Next, structure examples of the display device of this embodiment willbe described with reference to FIG. 1, FIG. 2, FIG. 3, and FIGS. 4A and4B.

Structure Example 1

FIG. 1 is a schematic perspective view of a display device 300. In thedisplay device 300, a substrate 351 and a substrate 361 are bonded toeach other. In FIG. 1, the substrate 361 is denoted by dashed lines.

The display device 300 includes a display portion 362, a circuit 364, awiring 365, and the like. FIG. 1 illustrates an example in which thedisplay device 300 is provided with an integrated circuit (IC) 373 andan FPC 372. Thus, the structure illustrated in FIG. 1 can be regarded asa display module including the display device 300, the IC, and the FPC.

As the circuit 364, for example, a scan line driver circuit can be used.

The wiring 365 has a function of supplying a signal and power to thedisplay portion 362 and the circuit 364. The signal and power are inputto the wiring 365 from the outside through the FPC 372 or from the IC373.

FIG. 1 illustrates an example in which the IC 373 is provided over thesubstrate 351 by a chip on glass (COG) method, a chip on film (COF)method, or the like. An IC including a scan line driver circuit, asignal line driver circuit, or the like can be used as the IC 373, forexample. Note that the display device 300 and the display module are notnecessarily provided with an IC. The IC may be mounted on the FPC by aCOF method or the like.

FIG. 1 illustrates an enlarged view of part of the display portion 362.Electrodes 311 a included in a plurality of display elements arearranged in a matrix in the display portion 362. The electrodes 311 aeach have a function of reflecting visible light, and serve as areflective electrode of a liquid crystal element 180.

The method for manufacturing the display device of this embodimentincludes a separation step in which a transistor, a display element, andthe like formed over a formation substrate are peeled from the formationsubstrate.

In the separation step, the peeling is performed between the formationsubstrate and a separation layer.

In this embodiment, a conductive layer having a function of reflectingvisible light is used as the separation layer. The separation layer isprocessed into a conductive layer in the display device after beingexposed by the peeling. Specifically, the electrode 311 a serving as areflective electrode of the liquid crystal element 180 can be formedusing the separation layer.

In the case of forming the electrode 311 a using the separation layer,the removal of the separation layer is not required. In addition, aconductive film to be the electrode 311 a does not need to be formed ina different step than the separation layer. Accordingly, a manufacturingprocess can be simplified.

Examples of a material for the separation layer (i.e., a material forthe electrode 311 a) include nickel (Ni), titanium (Ti), and silver(Ag), and an alloy containing any of these elements. As an alloycontaining silver, for example, an alloy of silver and copper, an alloyof silver, palladium, and copper (also referred to as Ag—Pd—Cu or APC),or an alloy of silver and magnesium can be given.

The separation layer may be formed in contact with the formationsubstrate. In that case, separation occurs in the separation step at theinterface between the formation substrate and the separation layer. Whenthe separation layer is formed in contact with a glass substrate, thelayer hardly remains on the formation substrate after the peeling,leading to easy reuse of the formation substrate.

It is preferable to form a nickel film in contact with the glasssubstrate, for example. In that case, separation can occur in theseparation step at the interface between the glass substrate and thenickel film.

The separation layer may be formed over the formation substrate with aninsulating layer including one or more layers provided therebetween. Inthat case, separation occurs in the separation step at the interfacebetween the separation layer and an insulating layer in contact with theseparation layer.

It is preferable to form, for example, an insulating layer over theformation substrate and a titanium film in contact with the insulatinglayer. In that case, separation can occur in the separation step at theinterface between the insulating layer and the titanium film. Titaniumis preferably used for the separation layer because of its low price andeasy application to large substrates.

The electrode 311 a is preferably formed using a separation layercontaining silver, in which case the visible light reflectance can beincreased.

When the separation layer contains nickel, titanium, or the like, asurface of the separation layer does not particularly need to besubjected to treatment such as plasma treatment. Thus, the displaydevice can be manufactured through fewer steps at lower cost.

As described above, the display device of this embodiment can bemanufactured with high mass productivity at low cost. The details of themethod for manufacturing the display device will be described later.

As illustrated in FIG. 1, the electrode 311 a includes an opening 451.In addition, the display portion 362 includes a light-emitting element170 that is positioned closer to the substrate 351 than the electrode311 a. Light from the light-emitting element 170 is emitted to thesubstrate 361 side through the opening 451 in the electrode 311 a. Thearea of the light-emitting region of the light-emitting element 170 maybe equal to the area of the opening 451. One of the area of thelight-emitting region of the light-emitting element 170 and the area ofthe opening 451 is preferably larger than the other because a margin formisalignment can be increased. It is particularly preferable that thearea of the opening 451 be larger than the area of the light-emittingregion of the light-emitting element 170. When the area of the opening451 is small, part of light from the light-emitting element 170 isblocked by the electrode 311 a and cannot be extracted to the outside,in some cases. The opening 451 with a sufficiently large area can reducewaste of light emitted from the light-emitting element 170.

FIG. 2 illustrates an example of cross-sections of part of a regionincluding the FPC 372, part of a region including the circuit 364, andpart of a region including the display portion 362 of the display device300 illustrated in FIG. 1.

The display device 300 illustrated in FIG. 2 includes a transistor 201,a transistor 203, a transistor 205, a transistor 206, the liquid crystalelement 180, the light-emitting element 170, an insulating layer 220, acoloring layer 131, a coloring layer 134, and the like, between thesubstrate 351 and the substrate 361. The substrate 361 and theinsulating layer 220 are bonded to each other with an adhesive layer141. The substrate 351 and the insulating layer 220 are bonded to eachother with the adhesive layer 142.

The substrate 361 is provided with the coloring layer 131, alight-blocking layer 132, an insulating layer 121, an electrode 113functioning as a common electrode of the liquid crystal element 180, analignment film 133 b, an insulating layer 117, and the like. Apolarizing plate 135 is provided on an outer surface of the substrate361. The insulating layer 121 may have a function of a planarizationlayer. The insulating layer 121 enables the electrode 113 to have analmost flat surface, resulting in a uniform alignment state of a liquidcrystal layer 112. The insulating layer 117 serves as a spacer forholding a cell gap of the liquid crystal element 180. In the case wherethe insulating layer 117 transmits visible light, the insulating layer117 may be positioned to overlap with a display region of the liquidcrystal element 180.

The liquid crystal element 180 is a reflective liquid crystal element.The liquid crystal element 180 reflects light to the substrate 361 side.The liquid crystal element 180 has a stacked-layer structure of theelectrode 311 a, the liquid crystal layer 112, and the electrode 113.The electrode 311 a functions as a pixel electrode. The electrode 311 aincludes the opening 451. The electrode 113 functions as the commonelectrode. An alignment film 133 a is provided between the liquidcrystal layer 112 and the electrode 311 a. The alignment film 133 b isprovided between the liquid crystal layer 112 and the electrode 113.

In the liquid crystal element 180, the electrode 311 a has a function ofreflecting visible light, and the electrode 113 has a function oftransmitting visible light. Light entering from the substrate 361 sideis polarized by the polarizing plate 135, transmitted through theelectrode 113 and the liquid crystal layer 112, and reflected by theelectrode 311 a. Then, the light is transmitted through the liquidcrystal layer 112 and the electrode 113 again to reach the polarizingplate 135. In this case, alignment of a liquid crystal can be controlledwith a voltage that is applied between the electrode 311 a and theelectrode 113, and thus optical modulation of light can be controlled.In other words, the intensity of light emitted through the polarizingplate 135 can be controlled. Light excluding light in a particularwavelength region is absorbed by the coloring layer 131, and thus,emitted light is red light, for example.

The thickness of the liquid crystal layer 112 differs in a portion wherethe electrode 311 a is provided and in a portion where the electrode 311a is not provided. Specifically, in the liquid crystal layer 112, athickness T1 of the portion where the electrode 311 a is provided issmaller than a thickness T2 of the portion where the electrode 311 a isnot provided.

At a connection portion 207, the electrode 311 a is electricallyconnected to a conductive layer 222 a included in the transistor 206 viaa conductive layer 221 b. The transistor 206 has a function ofcontrolling the driving of the liquid crystal element 180.

A connection portion 252 is provided in part of a region where theadhesive layer 141 is provided. At the connection portion 252, aconductive layer 311 c is electrically connected to part of theelectrode 113 through a connector 243. The electrode 311 a and theconductive layer 311 c can be formed by processing the same conductivefilm. Accordingly, a signal or a potential input from the FPC 372connected to the substrate 351 side can be supplied to the electrode 113formed on the substrate 361 side through the connection portion 252.

As the connector 243, for example, a conductive particle can be used. Asthe conductive particle, a particle of an organic resin, silica, or thelike coated with a metal material can be used. It is preferable to usenickel or gold as the metal material because contact resistance can bedecreased. It is also preferable to use a particle coated with layers oftwo or more kinds of metal materials, such as a particle coated withnickel and further with gold. A material capable of elastic deformationor plastic deformation is preferably used for the connector 243. Asillustrated in FIG. 2, the connector 243, which is the conductiveparticle, has a shape that is vertically crushed in some cases. With thecrushed shape, the contact area between the connector 243 and aconductive layer electrically connected to the connector 243 can beincreased, thereby reducing contact resistance and suppressing thegeneration of problems such as disconnection.

The connector 243 is preferably provided so as to be covered with theadhesive layer 141. For example, the connectors 243 can be dispersed inthe adhesive layer 141 before curing of the adhesive layer 141.

The light-emitting element 170 is a bottom-emission light-emittingelement. The light-emitting element 170 has a stacked-layer structure inwhich an electrode 191, an EL layer 192, and an electrode 193 arestacked in this order from the insulating layer 220 side. The electrode191 functions as a pixel electrode. The EL layer 192 contains at least alight-emitting substance. The electrode 193 functions as a commonelectrode. The light-emitting element 170 is an electroluminescentelement that emits light to the substrate 361 side when voltage isapplied between the electrode 191 and the electrode 193.

The electrode 191 is connected to the conductive layer 222 a included inthe transistor 205 through an opening provided in an insulating layer212, an insulating layer 213, and an insulating layer 214. Thetransistor 205 has a function of controlling the driving of thelight-emitting element 170. An insulating layer 216 covers an endportion of the electrode 191.

The electrode 191 has a function of transmitting visible light. Theelectrode 193 preferably has a function of reflecting visible light.

The light-emitting element 170 is preferably covered with an insulatinglayer 194. In FIG. 2, the insulating layer 194 is provided in contactwith the electrode 193. The insulating layer 194 can prevent an impurityfrom entering the light-emitting element 170, leading to an increase inthe reliability of the light-emitting element 170. The insulating layer194 and the substrate 351 are bonded to each other with an adhesivelayer 142.

Light is emitted from the light-emitting element 170 to the substrate361 side through the coloring layer 134, the insulating layer 220, theopening 451, and the like.

The liquid crystal element 180 and the light-emitting element 170 canexhibit various colors when the color of the coloring layer varies amongpixels. The display device 300 can display a color image using theliquid crystal element 180. The display device 300 can display a colorimage using the light-emitting element 170.

The transistor 201, the transistor 203, the transistor 205, and thetransistor 206 are formed on a plane of the insulating layer 220 on thesubstrate 351 side. These transistors can be fabricated through the sameprocess.

A circuit electrically connected to the liquid crystal element 180 and acircuit electrically connected to the light-emitting element 170 arepreferably formed on the same plane. In that case, the thickness of thedisplay device can be smaller than that in the case where the twocircuits are formed on different planes. Furthermore, since twotransistors can be formed in the same process, a manufacturing processcan be simplified as compared to the case where two transistors areformed on different planes.

The electrode 311 a, which serves as the pixel electrode of the liquidcrystal element 180, is positioned on the opposite side of a gateinsulating layer (an insulating layer 211) included in the transistorsfrom the electrode 191, which serves as the pixel electrode of thelight-emitting element 170.

In the case where a transistor including an oxide semiconductor in itschannel formation region and having extremely low off-state current isused as the transistor 206 or in the case where a memory elementelectrically connected to the transistor 206 is used, for example, indisplaying a still image using the liquid crystal element 180, even ifwriting operation to a pixel is stopped, the gray level can bemaintained. In other words, an image can be kept displayed even with anextremely low frame rate. In one embodiment of the present invention,the frame rate can be extremely low and driving with low powerconsumption can be performed.

The transistor 203 is used for controlling whether the pixel is selectedor not (such a transistor is also referred to as a switching transistoror a selection transistor). The transistor 205 is used for controllingcurrent flowing to the light-emitting element 170 (such a transistor isalso referred to as a driving transistor).

Insulating layers such as the insulating layer 211, the insulating layer212, the insulating layer 213, and the insulating layer 214 are providedon the substrate 351 side of the insulating layer 220. Part of theinsulating layer 211 functions as a gate insulating layer of eachtransistor. The insulating layer 212 is provided to cover the transistor206 and the like. The insulating layer 213 is provided to cover thetransistor 205 and the like. The insulating layer 214 functions as aplanarization layer. Note that the number of insulating layers coveringthe transistor is not limited and may be one or two or more.

A material through which impurities such as water or hydrogen do noteasily diffuse is preferably used for at least one of the insulatinglayers that cover the transistors. This is because such an insulatinglayer can serve as a barrier film. Such a structure can effectivelysuppress diffusion of the impurities into the transistors from theoutside, and a highly reliable display device can be provided.

Each of the transistors 201, 203, 205, and 206 includes a conductivelayer 221 a functioning as a gate, the insulating layer 211 functioningas the gate insulating layer, the conductive layer 222 a and aconductive layer 222 b functioning as a source and a drain, and asemiconductor layer 231. Here, a plurality of layers obtained byprocessing the same conductive film are shown with the same hatchingpattern.

The transistor 201 and the transistor 205 each include a conductivelayer 223 functioning as a gate, in addition to the components of thetransistor 203 or the transistor 206.

The structure in which the semiconductor layer where a channel is formedis provided between two gates is used as an example of the transistors201 and 205. Such a structure enables the control of the thresholdvoltages of transistors. The two gates may be connected to each otherand supplied with the same signal to operate the transistors. Suchtransistors can have higher field-effect mobility and thus have higheron-state current than other transistors. Consequently, a circuit capableof high-speed operation can be obtained. Furthermore, the area occupiedby a circuit portion can be reduced. The use of the transistor havinghigh on-state current can reduce signal delay in wirings and can reducedisplay unevenness even in a display device in which the number ofwirings is increased because of increase in size or definition.

Alternatively, by supplying a potential for controlling the thresholdvoltage to one of the two gates and a potential for driving to theother, the threshold voltage of the transistors can be controlled.

There is no limitation of the structure of the transistors included inthe display device. The transistor included in the circuit 364 and thetransistor included in the display portion 362 may have the samestructure or different structures. A plurality of transistors includedin the circuit 364 may have the same structure or a combination of twoor more kinds of structures. Similarly, a plurality of transistorsincluded in the display portion 362 may have the same structure or acombination of two or more kinds of structures.

It is preferable to use a conductive material containing an oxide forthe conductive layer 223. A conductive film used for the conductivelayer 223 is formed under an atmosphere containing oxygen, wherebyoxygen can be supplied to the insulating layer 212. The proportion of anoxygen gas in a deposition gas is preferably higher than or equal to 90%and lower than or equal to 100%. Oxygen supplied to the insulating layer212 is then supplied to the semiconductor layer 231 by later heattreatment; as a result, oxygen vacancies in the semiconductor layer 231can be reduced.

It is particularly preferable to use a low-resistance oxidesemiconductor for the conductive layer 223. In that case, an insulatingfilm that releases hydrogen, such as a silicon nitride film, ispreferably used for the insulating layer 213, for example, becausehydrogen can be supplied to the conductive layer 223 during theformation of the insulating layer 213 or by heat treatment performedafter the formation of the insulating layer 213, which leads to aneffective reduction in the electric resistance of the conductive layer223.

The coloring layer 134 is provided in contact with the insulating layer213. The coloring layer 134 is covered with the insulating layer 214.

A connection portion 204 is provided in a region where the substrate 351and the substrate 361 do not overlap with each other. In the connectionportion 204, the wiring 365 is electrically connected to the FPC 372 viaa connection layer 242. The connection portion 204 has a similarstructure to the connection portion 207. On the top surface of theconnection portion 204, a conductive layer 311 b is exposed. Theelectrode 311 a and the conductive layer 311 b are formed by processingthe same conductive film. The connection layer 242 is preferablyprovided to cover an end portion of the conductive layer 311 b.Accordingly, the connection portion 204 and the FPC 372 can beelectrically connected to each other via the connection layer 242.

As the polarizing plate 135 provided on the outer surface of thesubstrate 361, a linear polarizing plate or a circularly polarizingplate can be used. An example of a circularly polarizing plate is astack including a linear polarizing plate and a quarter-wave retardationplate. Such a structure can reduce reflection of external light. Thecell gap, alignment, drive voltage, and the like of the liquid crystalelement used as the liquid crystal element 180 are controlled dependingon the kind of the polarizing plate so that desirable contrast isobtained.

Note that a variety of optical members can be arranged on the outersurface of the substrate 361. Examples of the optical members include apolarizing plate, a retardation plate, a light diffusion layer (e.g., adiffusion film), an anti-reflective layer, and a light-condensing film.Furthermore, an antistatic film preventing the attachment of dust, awater repellent film suppressing the attachment of stain, a hard coatfilm suppressing generation of a scratch caused by the use, or the likemay be arranged on the outer surface of the substrate 361.

For each of the substrates 351 and 361, glass, quartz, ceramic,sapphire, an organic resin, or the like can be used. When the substrates351 and 361 are formed using a flexible material, the flexibility of thedisplay device can be increased. In particular, when the substrates 351and 361 are formed using an organic resin, the thickness and weight ofthe display device can be reduced.

A liquid crystal element having, for example, a vertical alignment (VA)mode can be used as the liquid crystal element 180. Examples of thevertical alignment mode include a multi-domain vertical alignment (MVA)mode, a patterned vertical alignment (PVA) mode, and an advanced superview (ASV) mode.

A liquid crystal element having a variety of modes can be used as theliquid crystal element 180. For example, a liquid crystal element using,instead of a VA mode, a twisted nematic (TN) mode, an in-plane switching(IPS) mode, a fringe field switching (FFS) mode, an axially symmetricaligned micro-cell (ASM) mode, an optically compensated birefringence(OCB) mode, a ferroelectric liquid crystal (FLC) mode, anantiferroelectric liquid crystal (AFLC) mode, or the like can be used.

The liquid crystal element is an element that controls transmission ornon-transmission of light utilizing an optical modulation action of theliquid crystal. The optical modulation action of the liquid crystal iscontrolled by an electric field applied to the liquid crystal (includinga horizontal electric field, a vertical electric field, and an obliqueelectric field). As the liquid crystal used for the liquid crystalelement, a thermotropic liquid crystal, a low-molecular liquid crystal,a high-molecular liquid crystal, a polymer dispersed liquid crystal(PDLC), a ferroelectric liquid crystal, an anti-ferroelectric liquidcrystal, or the like can be used. Such a liquid crystal materialexhibits a cholesteric phase, a smectic phase, a cubic phase, a chiralnematic phase, an isotropic phase, or the like depending on conditions.

As the liquid crystal material, a positive liquid crystal or a negativeliquid crystal may be used, and an appropriate liquid crystal materialcan be used depending on the mode or design to be used.

To control the alignment of the liquid crystal, the alignment films canbe provided. In the case where a horizontal electric field mode isemployed, a liquid crystal exhibiting a blue phase for which analignment film is unnecessary may be used. The blue phase is one ofliquid crystal phases, which is generated just before a cholestericphase changes into an isotropic phase while the temperature of acholesteric liquid crystal is increased. Since the blue phase appearsonly in a narrow temperature range, a liquid crystal composition inwhich several weight percent or more of a chiral material is mixed isused for the liquid crystal in order to improve the temperature range.The liquid crystal composition that includes a liquid crystal exhibitinga blue phase and a chiral material has a short response time and hasoptical isotropy. In addition, the liquid crystal composition thatincludes a liquid crystal exhibiting a blue phase and a chiral materialdoes not need alignment treatment and has small viewing angledependence. An alignment film does not need to be provided and rubbingtreatment is thus not necessary; accordingly, electrostatic dischargedamage caused by the rubbing treatment can be prevented and defects anddamage of the liquid crystal display device in the manufacturing processcan be reduced.

In the case where the reflective liquid crystal element is used, thepolarizing plate 135 is provided on the display surface side. Inaddition, a light diffusion plate is preferably provided on the displaysurface side to improve visibility.

A front light may be provided on the outer side of the polarizing plate135. As the front light, an edge-light front light is preferably used. Afront light including an LED is preferably used to reduce powerconsumption.

As the adhesive layer, any of a variety of curable adhesives such as areactive curable adhesive, a thermosetting adhesive, an anaerobicadhesive, and a photocurable adhesive such as an ultraviolet curableadhesive can be used. Examples of these adhesives include an epoxyresin, an acrylic resin, a silicone resin, a phenol resin, a polyimideresin, an imide resin, a polyvinyl chloride (PVC) resin, a polyvinylbutyral (PVB) resin, and an ethylene vinyl acetate (EVA) resin. Inparticular, a material with low moisture permeability, such as an epoxyresin, is preferred. Alternatively, a two-component-mixture-type resinmay be used. Further alternatively, an adhesive sheet or the like may beused.

As the connection layer 242, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

The light-emitting element 170 may be a top emission, bottom emission,or dual emission light-emitting element, or the like. A conductive filmthat transmits visible light is used as the electrode through whichlight is extracted. A conductive film that reflects visible light ispreferably used as the electrode through which light is not extracted.

The EL layer 192 includes at least a light-emitting layer. In additionto the light-emitting layer, the EL layer 192 may further include one ormore layers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with a high electron- andhole-transport property), and the like.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer 192, and an inorganic compound may also be included.The layers included in the EL layer 192 can be formed by any of thefollowing methods: an evaporation method (including a vacuum evaporationmethod), a transfer method, a printing method, an inkjet method, acoating method, and the like.

The EL layer 192 may contain an inorganic compound such as quantum dots.When quantum dots are used for the light-emitting layer, quantum dotscan function as light-emitting materials, for example.

With the use of the combination of a color filter (coloring layer) and amicrocavity structure (optical adjustment layer), light with high colorpurity can be extracted from the display device. The thickness of theoptical adjustment layer varies depending on the color of the pixel.

As materials for a gate, a source, and a drain of a transistor, and aconductive layer such as a wiring or an electrode included in a displaydevice, any of metals such as aluminum, titanium, chromium, nickel,copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten,or an alloy containing any of these metals as its main component can beused. A single-layer structure or multi-layer structure including a filmcontaining any of these materials can be used.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide (ITO), indium zinc oxide, zinc oxide, orzinc oxide containing gallium, or graphene can be used. Alternatively, ametal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium, or an alloy material containing any of these metal materialscan be used. Alternatively, a nitride of the metal material (e.g.,titanium nitride) or the like may be used. In the case of using themetal material or the alloy material (or the nitride thereof), thethickness is set small enough to be able to transmit light.Alternatively, a stacked film of any of the above materials can be usedfor the conductive layers. For example, a stacked film of indium tinoxide and an alloy of silver and magnesium is preferably used becausethe conductivity can be increased. They can also be used for conductivelayers such as a variety of wirings and electrodes included in a displaydevice, and conductive layers (e.g., conductive layers serving as apixel electrode or a common electrode) included in a display element.

Examples of an insulating material that can be used for the insulatinglayers include a resin such as acrylic or epoxy resin, and an inorganicinsulating material such as silicon oxide, silicon oxynitride, siliconnitride oxide, silicon nitride, or aluminum oxide.

Examples of a material that can be used for the coloring layers includea metal material, a resin material, and a resin material containing apigment or dye.

Structure Example 2

A display device 300A illustrated in FIG. 3 is different from thedisplay device 300 mainly in that a transistor 281, a transistor 284, atransistor 285, and a transistor 286 are included instead of thetransistor 201, the transistor 203, the transistor 205, and thetransistor 206.

Note that the positions of the insulating layer 117, the connectionportion 207, and the like in FIG. 3 are different from those in FIG. 2.FIG. 3 illustrates an end portion of a pixel. The insulating layer 117is provided so as to overlap with an end portion of the coloring layer131 and an end portion of the light-blocking layer 132. As in thisstructure, at least part of the insulating layer 117 may be provided ina region not overlapping with a display region (or in a regionoverlapping with the light-blocking layer 132).

Two transistors included in the display device may partly overlap witheach other like the transistor 284 and the transistor 285. In that case,the area occupied by a pixel circuit can be reduced, leading to anincrease in resolution. Furthermore, the light-emitting area of thelight-emitting element 170 can be increased, leading to an improvementin aperture ratio. The light-emitting element 170 with a high apertureratio requires low current density to obtain necessary luminance; thus,the reliability is improved.

Each of the transistors 281, 284, and 286 includes the conductive layer221 a, the insulating layer 211, the semiconductor layer 231, theconductive layer 222 a, and the conductive layer 222 b. The conductivelayer 221 a overlaps with the semiconductor layer 231 with theinsulating layer 211 positioned therebetween. The conductive layer 222 aand the conductive layer 222 b are electrically connected to thesemiconductor layer 231. The transistor 281 includes the conductivelayer 223.

The transistor 285 includes the conductive layer 222 a, an insulatinglayer 217, a semiconductor layer 261, the conductive layer 223, theinsulating layer 212, the insulating layer 213, a conductive layer 263a, and a conductive layer 263 b. The conductive layer 222 a overlapswith the semiconductor layer 261 with the insulating layer 217positioned therebetween. The conductive layer 223 overlaps with thesemiconductor layer 261 with the insulating layers 212 and 213positioned therebetween. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261.

The conductive layer 221 a functions as a gate. The insulating layer 211functions as a gate insulating layer. The conductive layer 222 afunctions as one of a source and a drain. The conductive layer 222 bincluded in the transistor 286 functions as the other of the source andthe drain.

The conductive layer 222 a shared by the transistor 284 and thetransistor 285 has a portion functioning as one of a source and a drainof the transistor 284 and a portion functioning as a gate of thetransistor 285. The insulating layer 217, the insulating layer 212, andthe insulating layer 213 function as gate insulating layers. One of theconductive layer 263 a and the conductive layer 263 b functions as asource and the other functions as a drain. The conductive layer 223functions as a gate.

Structure Example 3

FIG. 4A is a cross-sectional view illustrating a display portion of adisplay device 300B.

The display device 300B is different from the display device 300 in thatthe coloring layer 131 is not provided. The transistor 203 is notillustrated in FIG. 4A. Other components are similar to those of thedisplay device 300 and thus are not described in detail.

The liquid crystal element 180 emits white light. Since the coloringlayer 131 is not provided, the display device 300B can display ablack-and-white image or a grayscale image using the liquid crystalelement 180.

The display device 300B is an example in which the substrate 361 isprovided with the electrode 113 with the insulating layer 121 positionedtherebetween. The insulating layer 121 is not necessarily provided, andthe electrode 113 may be provided in contact with the substrate 361 asin a display device 300C illustrated in FIG. 4B.

Structure Example 4

The display device 300C illustrated in FIG. 4B is different from thedisplay device 300B in that the EL layer 192 is separately provided foreach color and in that the coloring layer 134 and the insulating layer121 are not provided. Other components are similar to those of thedisplay device 300B and thus are not described in detail.

In the light-emitting element 170 employing a separate coloring method,at least one layer (typified by the light-emitting layer) included inthe EL layer 192 is separately provided for each color. All layersincluded in the EL layer may be separately provided for each color.

Example 1 of Manufacturing Method of Display Device

Next, the method for manufacturing the display device of this embodimentwill be specifically described with reference to FIGS. 5A, 5B1, 5B2, and5C, FIGS. 6A to 6C, FIGS. 7A to 7C, and FIGS. 8A and 8B. An example of amanufacturing method of the display device 300 illustrated in FIG. 2will be described below. The manufacturing method will be described withreference to FIGS. 5A, 5B1, 5B2, and 5C, FIGS. 6A to 6C, FIGS. 7A to 7C,and FIGS. 8A and 8B, focusing on the display portion 362 and theconnection portion 204 of the display device 300. Note that thetransistor 203 is not illustrated in FIGS. 5A, 5B1, 5B2, and 5C, FIGS.6A to 6C, FIGS. 7A to 7C, and FIGS. 8A and 8B.

Thin films included in the display device (e.g., insulating films,semiconductor films, or conductive films) can be formed by any of asputtering method, a chemical vapor deposition (CVD) method, a vacuumevaporation method, a pulsed laser deposition (PLD) method, an atomiclayer deposition (ALD) method, and the like. As the CVD method, aplasma-enhanced chemical vapor deposition (PECVD) method or a thermalCVD method may be used. As the thermal CVD method, for example, a metalorganic chemical vapor deposition (MOCVD) method may be used.

Alternatively, thin films included in the display device (e.g.,insulating films, semiconductor films, or conductive films) can beformed by a method such as spin coating, dipping, spray coating,ink-jetting, dispensing, screen printing, or offset printing, or with adoctor knife, a slit coater, a roll coater, a curtain coater, or a knifecoater.

When thin films included in the display device are processed, alithography method or the like can be used for the processing.Alternatively, island-shaped thin films may be formed by a filmformation method using a blocking mask. A nanoimprinting method, asandblasting method, a lift-off method, or the like may be used for theprocessing of thin films. Examples of a photolithography method includea method in which a resist mask is formed over a thin film to beprocessed, the thin film is processed by etching or the like, and theresist mask is removed, and a method in which a photosensitive thin filmis formed and exposed to light and developed to be processed into adesired shape.

In the case of using light in the lithography method, any of an i-line(light with a wavelength of 365 nm), a g-line (light with a wavelengthof 436 nm), and an h-line (light with a wavelength of 405 nm), orcombined light of any of them can be used for exposure. Alternatively,ultraviolet light, KrF laser light, ArF laser light, or the like can beused. Exposure may be performed by liquid immersion exposure technique.As the light for the exposure, extreme ultra-violet (EUV) light orX-rays may be used. Instead of the light for the exposure, an electronbeam can be used. It is preferable to use EUV, X-rays, or an electronbeam because extremely minute processing can be performed. Note that inthe case of performing exposure by scanning of a beam such as anelectron beam, a photomask is not needed.

For etching of thin films, a dry etching method, a wet etching method, asandblast method, or the like can be used.

First, the coloring layer 131 is formed over the substrate 361 (FIG.5A). The coloring layer 131 is formed using a photosensitive material,in which case the processing into an island shape can be performed by aphotolithography method or the like. Note that in the circuit 364 andthe like illustrated in FIG. 2, the light-blocking layer 132 is providedover the substrate 361.

Then, the insulating layer 121 is formed over the coloring layer 131 andthe light-blocking layer 132.

The insulating layer 121 preferably functions as a planarization layer.An organic insulating film is preferably used for the insulating layer121. A resin such as acrylic or epoxy is suitably used for theinsulating layer 121.

An inorganic insulating film may be used for the insulating layer 121.For example, an inorganic insulating film such as a silicon nitridefilm, a silicon oxynitride film, a silicon oxide film, a silicon nitrideoxide film, an aluminum oxide film, or an aluminum nitride film can beused for the insulating layer 121. Alternatively, a hafnium oxide film,an yttrium oxide film, a zirconium oxide film, a gallium oxide film, atantalum oxide film, a magnesium oxide film, a lanthanum oxide film, acerium oxide film, a neodymium oxide film, or the like may be used.Further alternatively, a stack including two or more of the aboveinsulating films may be used.

Next, the electrode 113 is formed. The electrode 113 can be formed inthe following manner: a conductive film is formed, a resist mask isformed, the conductive film is etched, and the resist mask is removed.The electrode 113 is formed using a conductive material that transmitsvisible light.

After that, the insulating layer 117 is formed over the electrode 113.An organic insulating film is preferably used for the insulating layer117. A resin such as acrylic or epoxy is suitably used for theinsulating layer 117.

Subsequently, the alignment film 133 b is formed over the electrode 113and the insulating layer 117 (FIG. 5A). The alignment film 133 b can beformed in the following manner: a thin film is formed using a resin orthe like, and then, rubbing treatment is performed.

Note that steps illustrated in FIGS. 5B1, 5B2, and 5C, FIGS. 6A to 6C,FIGS. 7A to 7C, and FIG. 8A are performed independently of the stepsdescribed with reference to FIG. 5A.

First, a separation layer 311 is formed over a formation substrate 350(FIG. 5B1). In the step illustrated in FIG. 5B1, a material is selectedthat would cause separation at the interface between the formationsubstrate 350 and the separation layer 311 when the formation substrate350 is peeled.

Alternatively, an insulating layer 355 is formed over the formationsubstrate 350 and the separation layer 311 is formed over the insulatinglayer 355 (FIG. 5B2). In the step illustrated in FIG. 5B2, a material isselected that would cause separation at the interface between theinsulating layer 355 and the separation layer 311 when the formationsubstrate 350 is peeled.

The formation substrate 350 has stiffness high enough for easy transferand has resistance to heat applied in the manufacturing process.Examples of a material that can be used for the formation substrate 350include glass, quartz, ceramic, sapphire, a resin, a semiconductor, ametal, and an alloy. Examples of the glass include alkali-free glass,barium borosilicate glass, and aluminoborosilicate glass.

The separation layer 311 can be formed using, for example, nickel (Ni),titanium (Ti), silver (Ag), or an alloy containing any of theseelements.

The position of an interface where peeling is performed in theseparation step depends on the material of the separation layer 311.Thus, the selection of the material of the separation layer 311 isimportant. For example, when tungsten (W) or molybdenum (Mo) is used forthe separation layer, the separation layer remains on the formationsubstrate side in many cases. In this embodiment, the separation layer311 is formed using nickel (Ni), titanium (Ti), silver (Ag), or an alloycontaining any of these elements. The use of such a material allowsseparation between the formation substrate 350 and the separation layer311 at the time of peeling (the separation layer 311 hardly remains onthe formation substrate 350 side).

In Example 1 of manufacturing method of display device, the electrode311 a is formed using the separation layer 311 in a later step; thus, itis preferable to use a material with high visible light reflexibilityfor the separation layer 311.

The thickness of the separation layer 311 is preferably greater than orequal to 10 nm and less than or equal to 1000 nm, and further preferablygreater than or equal to 10 nm and less than or equal to 500 nm.

When a glass substrate is used for the formation substrate 350 and anickel film is used for the separation layer 311 in FIG. 5B1, forexample, separation can occur in the separation step at the interfacebetween the formation substrate 350 and the separation layer 311. Thepeelability can be increased particularly when the maximum temperatureapplied to the separation layer 311 is higher than 150° C. and lowerthan 450° C., preferably higher than or equal to 200° C. and lower thanor equal to 400° C., and further preferably higher than or equal to 250°C. and lower than or equal to 350° C. For this reason, the maximumtemperature applied to the separation layer 311 in steps of forming atransistor and a display element over the separation layer 311 ispreferably within the above range.

When the insulating layer 355 has a three-layer structure describedbelow and a titanium film is used for the separation layer 311 in FIG.5B2, for example, separation can be caused in the separation step at theinterface between the insulating layer 355 and the separation layer 311.

In the case where a titanium film is used for the separation layer 311and an oxide film (an oxide insulating film or an oxide conductive filmsuch as an ITO film or the like) is formed on the titanium film, thequality of the separation layer 311 is changed (e.g., titanium isoxidized) and the peelability is decreased when the temperature of alater heating step is too high, in some cases. The quality change intitanium can be inhibited and the peelability can be increased when themaximum temperature applied to the separation layer 311 is lower than450° C., preferably lower than or equal to 400° C., and furtherpreferably lower than or equal to 350° C. For this reason, the maximumtemperature applied to the separation layer 311 in the steps of formingthe transistor and the display element over the separation layer 311 ispreferably within the above range.

The insulating layer 355 preferably includes a first insulating layerover the formation substrate 350, a second insulating layer over thefirst insulating layer, and a third insulating layer over the secondinsulating layer, for example.

The first insulating layer has a function of blocking hydrogen andfluorine (and nitrogen) released from the second insulating layer andthe third insulating layer in the later heating step.

The first insulating layer preferably contains nitrogen and silicon. Forthe first insulating layer, for example, a silicon nitride film, asilicon oxynitride film, or a silicon nitride oxide film can be used. Itis particularly preferable to use a silicon nitride film or a siliconnitride oxide film.

The first insulating layer can be formed by a sputtering method, aplasma CVD method, or the like. For the first insulating layer, forexample, a silicon nitride film is formed by a plasma CVD method using adeposition gas containing a silane (SiH₄) gas, a hydrogen gas, and anammonia (NH₃) gas.

There is no particular limitation on the thickness of the firstinsulating layer. The thickness can be greater than or equal to 50 nmand less than or equal to 600 nm, and preferably greater than or equalto 100 nm and less than or equal to 300 nm, for example.

Note that in the case where the formation substrate has a sufficientlyhigh blocking property against hydrogen and fluorine (and nitrogen), thefirst insulating layer does not always need to be provided. In thatcase, the second insulating layer may be provided on the formationsubstrate.

The second insulating layer has a function of releasing hydrogen in thelater heating step. The second insulating layer may also have a functionof releasing hydrogen and nitrogen in the later heating step.

The second insulating layer preferably contains oxygen and silicon. Itis preferable that the second insulating layer further contain hydrogen.It is preferable that the second insulating layer further containnitrogen. For the second insulating layer, for example, a silicon oxidefilm, a silicon nitride film, a silicon oxynitride film, or a siliconnitride oxide film can be used.

The second insulating layer can be formed by a sputtering method, aplasma CVD method, or the like. It is particularly preferable to formthe silicon oxynitride film by a plasma CVD method using a depositiongas containing a silane gas and a nitrous oxide (N₂O) gas because alarge amount of hydrogen and nitrogen can be contained in the film. Inaddition, the proportion of the silane gas in the deposition gas ispreferably higher, in which case the amount of released hydrogen in thelater heating step is increased.

The thickness of the second insulating layer is preferably larger for anincrease in the amount of released hydrogen and nitrogen; however, thethickness is preferably determined in consideration of productivity. Thethickness of the second insulating layer is preferably greater than orequal to 1 nm and less than or equal to 1 μm, further preferably greaterthan or equal to 50 nm and less than or equal to 800 nm, still furtherpreferably greater than or equal to 100 nm and less than or equal to 600nm, and particularly preferably greater than or equal to 200 nm and lessthan or equal to 400 nm.

At least one of the first insulating layer and the second insulatinglayer can serve as a base film. In the case where a glass substrate isused as the formation substrate 350, for example, a base film ispreferably provided between the formation substrate 350 and theseparation layer 311 because contamination from the glass substrate canbe prevented.

The third insulating layer has a function of releasing fluorine in thelater heating step. The third insulating layer also has a function ofallowing hydrogen (and nitrogen) released from the second insulatinglayer to pass through.

The third insulating layer preferably contains oxygen, fluorine, andsilicon. For the third insulating layer, for example, a silicon oxidefilm containing fluorine (SiOF) can be used.

The third insulating layer can be formed by a sputtering method, aplasma CVD method, or the like. For the third insulating layer, forexample, a silicon oxide film containing fluorine is formed by a plasmaCVD method using a deposition gas containing a silane gas, a nitrousoxide gas, and a silicon tetrafluoride (SiF₄) gas.

The third insulating layer preferably has a thickness greater than orequal to 1 nm and less than or equal to 500 nm, further preferablygreater than or equal to 10 nm and less than or equal to 300 nm, andstill further preferably greater than or equal to 10 nm and less than orequal to 200 nm. The third insulating layer can have a smaller thicknessthan the second insulating layer.

After the insulating layer 355 and the separation layer 311 are formedover the formation substrate 350, heat treatment is performed. The heattreatment is preferably performed after the insulating layer 220 isformed over the separation layer 311. For example, the heat treatment ispreferably performed after the insulating layer 220 is formed before thetransistor is formed. Heat treatment performed in the step of formingthe transistor may serve as this heat treatment.

Owing to the heat treatment, hydrogen (and nitrogen) is released fromthe second insulating layer and supplied to the separation layer 311 (orthe interface between the third insulating layer and the separationlayer 311) through the third insulating layer. In addition, fluorine isreleased from the third insulating layer and supplied to the separationlayer 311 (or the interface between the third insulating layer and theseparation layer 311). At this time, the first insulating layer and theinsulating layer 220 block the released hydrogen and fluorine (andnitrogen), leading to efficient supply of hydrogen and fluorine (andnitrogen) to the separation layer 311 (or the interface between thethird insulating layer and the separation layer 311).

The atmosphere in which the heat treatment is performed is notparticularly limited and may be an air atmosphere. It is preferable toperform the heat treatment in an inert gas atmosphere such as a nitrogenatmosphere or a rare gas atmosphere.

The following description is for the case of employing the stepillustrated in FIG. 5B1. Note that the following description can also beapplied to the case of employing the step illustrated in FIG. 5B2.

The insulating layer 220 is formed (FIG. 5C). Then, openings that reachthe separation layer 311 are provided in the insulating layer 220. Toprevent the separation layer 311 from being removed, it is preferablethat the etching selectivity ratio of the insulating layer 220 to theseparation layer 311 be sufficiently large.

The insulating layer 220 can be used as a barrier layer that preventsdiffusion of impurities into the transistor and the display elementformed later.

The insulating layer 220 can be formed using the inorganic insulatingfilm, the resin, or the like that can be used for the insulating layer121. It is particularly preferable to use a silicon nitride film.

Next, the connection portion 204, the connection portion 207, thetransistor 205, and the transistor 206 are formed over the insulatinglayer 220.

There is no particular limitation on a semiconductor material used for asemiconductor layer of the transistor, and for example, a Group 14element, a compound semiconductor, or an oxide semiconductor can beused. Typically, a semiconductor containing silicon, a semiconductorcontaining gallium arsenide, an oxide semiconductor containing indium,or the like can be used.

It is preferable to use an oxide semiconductor for a channel formationregion of the transistor. With the use of an oxide semiconductor, themaximum process temperature can be lower than that in the case of usinglow-temperature polysilicon (LTPS). Specifically, the transistor formedusing an oxide semiconductor does not require heat treatment at hightemperatures unlike a transistor formed using LTPS, and can be formed ata temperature lower than or equal to 350° C., or even lower than orequal to 300° C. Even without heat treatment at high temperatures, ahighly reliable transistor can be formed and the peelability between theformation substrate 350 (typified by a glass substrate) and theseparation layer 311 (typified by nickel) can be increased. Furthermore,even without heat treatment at high temperatures, a highly reliabletransistor can be formed, the quality change in the separation layer 311(typified by titanium) can be inhibited, and the peelability can beincreased.

Here, the case where a bottom-gate transistor including an oxidesemiconductor layer as the semiconductor layer 231 is fabricated as thetransistor 206 is described. The transistor 205 includes the conductivelayer 223 and the insulating layer 212 in addition to the components ofthe transistor 206, and has two gates.

An oxide semiconductor is preferably used for the semiconductor layer ofthe transistor. The use of a semiconductor material having a wider bandgap and a lower carrier density than silicon can reduce off-statecurrent of the transistor.

Specifically, first, the conductive layer 221 a, the conductive layer221 b, and a conductive layer 221 c are formed over the insulating layer220. The conductive layer 221 a, the conductive layer 221 b, and theconductive layer 221 c can be formed in the following manner: aconductive film is formed, a resist mask is formed, the conductive filmis etched, and the resist mask is removed. At this time, the conductivelayer 221 b and the separation layer 311 are connected to each otherthrough an opening in the insulating layer 220 at the connection portion207, and the conductive layer 221 c and the separation layer 311 areconnected to each other through an opening in the insulating layer 220at the connection portion 204.

When the conductive layer 221 b and the conductive layer 221 c areconnected to the separation layer 311, an adverse effect ofelectrostatic charge due to peeling can be inhibited.

Next, the insulating layer 211 is formed.

For the insulating layer 211, an inorganic insulating film such as asilicon nitride film, a silicon oxynitride film, a silicon oxide film, asilicon nitride oxide film, an aluminum oxide film, or an aluminumnitride film can be used, for example. Alternatively, a hafnium oxidefilm, an yttrium oxide film, a zirconium oxide film, a gallium oxidefilm, a tantalum oxide film, a magnesium oxide film, a lanthanum oxidefilm, a cerium oxide film, a neodymium oxide film, or the like may beused. Further alternatively, a stack including two or more of the aboveinsulating films may be used.

An inorganic insulating film is preferably formed at high temperaturesbecause the film can have higher density and a higher barrier propertyas the deposition temperature becomes higher. The substrate temperatureduring the deposition of the inorganic insulating film is preferablyhigher than or equal to room temperature (25° C.) and lower than orequal to 350° C., and further preferably higher than or equal to 100° C.and lower than or equal to 300° C.

Then, the semiconductor layer 231 is formed. In this embodiment, anoxide semiconductor layer is formed as the semiconductor layer 231. Theoxide semiconductor layer can be formed in the following manner: anoxide semiconductor film is formed, a resist mask is formed, the oxidesemiconductor film is etched, and the resist mask is removed.

The substrate temperature during the deposition of the oxidesemiconductor film is preferably lower than or equal to 350° C., furtherpreferably higher than or equal to room temperature and lower than orequal to 200° C., and still further preferably higher than or equal toroom temperature and lower than or equal to 130° C.

The oxide semiconductor film can be formed using one or both of an inertgas and an oxygen gas. Note that there is no particular limitation onthe percentage of oxygen flow rate (partial pressure of oxygen) at thetime of forming the oxide semiconductor film. To fabricate a transistorhaving high field-effect mobility, however, the percentage of oxygenflow rate (partial pressure of oxygen) at the time of forming the oxidesemiconductor film is preferably higher than or equal to 0% and lowerthan or equal to 30%, further preferably higher than or equal to 5% andlower than or equal to 30%, and still further preferably higher than orequal to 7% and lower than or equal to 15%.

The oxide semiconductor film preferably contains at least indium orzinc. It is particularly preferable to contain indium and zinc.

The energy gap of the oxide semiconductor is preferably 2 eV or more,further preferably 2.5 eV or more, and still further preferably 3 eV ormore. The use of such an oxide semiconductor having a wide energy gapleads to a reduction in off-state current of a transistor.

The oxide semiconductor film can be formed by a sputtering method.Alternatively, a PLD method, a PECVD method, a thermal CVD method, anALD method, a vacuum evaporation method, or the like may be used.

Note that an example of an oxide semiconductor will be described inEmbodiment 3.

Next, the conductive layers 222 a and 222 b and the wiring 365 areformed. The conductive layers 222 a and 222 b and the wiring 365 can beformed in the following manner: a conductive film is formed, a resistmask is formed, the conductive film is etched, and the resist mask isremoved. Each of the conductive layers 222 a and 222 b is connected tothe semiconductor layer 231. Here, the conductive layer 222 a includedin the transistor 206 is electrically connected to the conductive layer221 b. As a result, the separation layer 311 and the conductive layer222 a can be electrically connected to each other at the connectionportion 207. At the connection portion 204, the wiring 365 and theseparation layer 311 are electrically connected to each other with theconductive layer 221 c provided therebetween.

Note that during the processing of the conductive layer 222 a and theconductive layer 222 b, the semiconductor layer 231 might be partlyetched to be thin in a region not covered by the resist mask.

In the above manner, the transistor 206 can be fabricated (FIG. 5C). Inthe transistor 206, part of the conductive layer 221 a functions as agate, part of the insulating layer 211 functions as a gate insulatinglayer, and the conductive layer 222 a and the conductive layer 222 beach function as one of a source and a drain.

Next, the insulating layer 212 that covers the transistor 206 is formed,and the conductive layer 223 is formed over the insulating layer 212.

The insulating layer 212 can be formed in a manner similar to that ofthe insulating layer 211.

The conductive layer 223 included in the transistor 205 can be formed inthe following manner: a conductive film is formed, a resist mask isformed, the conductive film is etched, and the resist mask is removed.

In the above manner, the transistor 205 can be fabricated (FIG. 5C). Inthe transistor 205, part of the conductive layer 221 a and part of theconductive layer 223 function as gates, part of the insulating layer 211and part of the insulating layer 212 function as gate insulating layers,and the conductive layer 222 a and the conductive layer 222 b eachfunction as a source or a drain.

Next, the insulating layer 213 is formed (FIG. 5C). The insulating layer213 can be formed in a manner similar to that of the insulating layer211.

It is preferable to use an oxide insulating film formed in an atmospherecontaining oxygen, such as a silicon oxide film or a silicon oxynitridefilm, for the insulating layer 212. An insulating film with low oxygendiffusibility and oxygen permeability, such as a silicon nitride film,is preferably stacked as the insulating layer 213 over the silicon oxidefilm or the silicon oxynitride film. The oxide insulating film formed inan atmosphere containing oxygen can easily release a large amount ofoxygen by heating. When a stack including such an oxide insulating filmthat releases oxygen and an insulating film with low oxygendiffusibility and oxygen permeability is heated, oxygen can be suppliedto the oxide semiconductor layer. As a result, oxygen vacancies in theoxide semiconductor layer can be filled and defects at the interfacebetween the oxide semiconductor layer and the insulating layer 212 canbe repaired, leading to a reduction in defect levels. Accordingly, anextremely highly reliable display device can be fabricated.

Next, the coloring layer 134 is formed over the insulating layer 213(FIG. 5C), and then, the insulating layer 214 is formed (FIG. 6A).

The coloring layer 134 can be formed in a manner similar to that of thecoloring layer 131. The display element is formed on the insulatinglayer 214 in a later step; thus, the insulating layer 214 preferablyfunctions as a planarization layer. For the insulating layer 214, thedescription of the resin or the inorganic insulating film that can beused for the insulating layer 121 can be referred to.

After that, an opening that reaches the conductive layer 222 a includedin the transistor 205 is formed in the insulating layer 212, theinsulating layer 213, and the insulating layer 214.

Subsequently, the electrode 191 is formed (FIG. 6A). The electrode 191can be formed in the following manner: a conductive film is formed, aresist mask is formed, the conductive film is etched, and the resistmask is removed. Here, the conductive layer 222 a included in thetransistor 205 and the electrode 191 are connected to each other. Theelectrode 191 is formed using a conductive material that transmitsvisible light.

Then, the insulating layer 216 that covers the end portion of theelectrode 191 is formed (FIG. 6A). For the insulating layer 216, thedescription of the resin or the inorganic insulating film that can beused for the insulating layer 121 can be referred to. The insulatinglayer 216 includes an opening in a region overlapping with the electrode191.

Next, the EL layer 192 and the electrode 193 are formed (FIG. 6B). Partof the electrode 193 functions as the common electrode of thelight-emitting element 170. The electrode 193 is formed using aconductive material that reflects visible light.

The EL layer 192 can be formed by an evaporation method, a coatingmethod, a printing method, a discharge method, or the like. In the casewhere the EL layer 192 is formed for each individual pixel, anevaporation method using a blocking mask such as a metal mask, anink-jet method, or the like can be used. In the case of sharing the ELlayer 192 by some pixels, an evaporation method not using a metal maskcan be used.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer 192, and an inorganic compound may also be included.

Steps after the formation of the EL layer 192 are performed such thattemperatures higher than the heat resistant temperature of the EL layer192 are not applied to the EL layer 192. The electrode 193 can be formedby an evaporation method, a sputtering method, or the like.

In the above manner, the light-emitting element 170 can be formed (FIG.6B). In the light-emitting element 170, the electrode 191 part of whichfunctions as the pixel electrode, the EL layer 192, and the electrode193 part of which functions as the common electrode are stacked. Thelight-emitting element 170 is formed such that the light-emitting regionoverlaps with the coloring layer 134.

Although an example where a bottom-emission light-emitting element isformed as the light-emitting element 170 is described here, oneembodiment of the present invention is not limited thereto.

The light-emitting element may be a top emission, bottom emission, ordual emission light-emitting element. A conductive film that transmitsvisible light is used as the electrode through which light is extracted.A conductive film that reflects visible light is preferably used as theelectrode through which light is not extracted.

Next, the insulating layer 194 is formed so as to cover the electrode193 (FIG. 6B). The insulating layer 194 functions as a protective layerthat prevents diffusion of impurities such as water into thelight-emitting element 170. The light-emitting element 170 is sealedwith the insulating layer 194. After the electrode 193 is formed, theinsulating layer 194 is preferably formed without exposure to the air.

The inorganic insulating film that can be used for the insulating layer121 can be used for the insulating layer 194, for example. It isparticularly preferable that an inorganic insulating film with a highbarrier property be included. A stack including an inorganic insulatingfilm and an organic insulating film can also be used.

The insulating layer 194 is preferably formed at substrate temperaturelower than or equal to the heat resistant temperature of the EL layer192. The insulating layer 194 can be formed by an ALD method, asputtering method, or the like. An ALD method and a sputtering methodare preferable because a film can be formed at low temperatures. An ALDmethod is preferable because the coverage of the insulating layer 194 isimproved.

Then, the substrate 351 is bonded to a surface of the insulating layer194 with the adhesive layer 142 (FIG. 6C).

As the adhesive layer 142, any of a variety of curable adhesives such asa reactive curable adhesive, a thermosetting adhesive, an anaerobicadhesive, and a photocurable adhesive such as an ultraviolet curableadhesive can be used. Alternatively, an adhesive sheet or the like maybe used.

For the substrate 351, a polyester resin such as polyethyleneterephthalate (PET) or polyethylene naphthalate (PEN), apolyacrylonitrile resin, an acrylic resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin (e.g., nylon or aramid),a polysiloxane resin, a cycloolefin resin, a polystyrene resin, apolyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin,a polyvinylidene chloride resin, a polypropylene resin, apolytetrafluoroethylene (PTFE) resin, an ABS resin, or cellulosenanofiber can be used, for example. Any of a variety of materials suchas glass, quartz, a resin, a metal, an alloy, and a semiconductor can beused for the substrate 351. The substrate 351 formed using any of avariety of materials such as glass, quartz, a resin, a metal, an alloy,and a semiconductor may be thin enough to be flexible.

After that, the formation substrate 350 is peeled (FIG. 7A).

The separation occurs at the interface between the separation layer 311and the formation substrate 350, so that the separation layer 311 isexposed (FIGS. 7A and 7B).

Note that in the case of employing the step illustrated in FIG. 5B2instead of the step illustrated in FIG. 5B1, the separation occurs atthe interface between the insulating layer 355 and the separation layer311.

Before the separation, a separation trigger may be formed in theseparation layer 311. For example, part of or the entire separationlayer 311 may be irradiated with laser light, in which case theseparation layer 311 can be embrittled or the adhesion between theseparation layer 311 and the formation substrate 350 can be reduced.

The formation substrate 350 can be peeled by applying a perpendiculartensile force to the separation layer 311, for example. Specifically,the formation substrate 350 can be peeled by pulling up the substrate351 by part of its suction-attached top surface.

The separation trigger may be formed by inserting a sharp instrumentsuch as a knife between the separation layer 311 and the formationsubstrate 350. Alternatively, the separation trigger may be formed bycutting the separation layer 311 from the substrate 351 side with asharp instrument.

Next, the separation layer 311 is processed into the electrode 311 a andthe conductive layer 311 b (FIG. 7C). The opening 451 overlapping withthe light-emitting region and the coloring layer 134 of thelight-emitting element 170 is provided in the electrode 311 a. Theelectrode 311 a and the conductive layer 311 b can be formed in thefollowing manner: a resist mask is formed over the separation layer 311,the separation layer 311 is etched, and the resist mask is removed. Theseparation layer 311 can be processed by wet etching or dry etching; itis particularly preferable to use dry etching. Note that the conductivelayer 311 c illustrated in FIG. 2 can be formed at the same time as theelectrode 311 a and the conductive layer 311 b by processing theseparation layer 311.

Subsequently, the alignment film 133 a is formed over the electrode 311a (FIG. 8A). The alignment film 133 a can be formed in the followingmanner: a thin film is formed using a resin or the like, and then,rubbing treatment is performed.

Then, the substrate 361 obtained through the steps described using FIG.5A and the substrate 351 obtained through the steps up to the stepillustrated in FIG. 8A are bonded to each other with the liquid crystallayer 112 provided therebetween (FIG. 8B). The substrate 351 and thesubstrate 361 are bonded to each other with the adhesive layer 141. Formaterials of the adhesive layer 141, the description of the materialsthat can be used for the adhesive layer 142 can be referred to. Notethat in the connection portion 252 illustrated in FIG. 2, the adhesivelayer 141 contains a conductive particle. Accordingly, the electrode 113and the conductive layer 311 c can be electrically connected to eachother when the substrate 351 and the substrate 361 are bonded to eachother.

In the liquid crystal element 180 illustrated in FIG. 8B, the electrode311 a part of which functions as the pixel electrode, the liquid crystallayer 112, and the electrode 113 part of which functions as the commonelectrode are stacked. The liquid crystal element 180 is formed so as tooverlap with the coloring layer 131.

Through the above steps, the display device 300 can be fabricated.

Note that the polarizing plate 135 is placed on the outer surface of thesubstrate 361.

The conductive layer 311 b is electrically connected to the FPC 372through the connection layer 242. As a result, the FPC 372 and thewiring 365 can be electrically connected to each other.

As described above, in Example 1 of manufacturing method of displaydevice, the surface of the separation layer does not particularly needto be subjected to treatment such as plasma treatment after theformation of the separation layer. Furthermore, a low-cost material canbe used for the separation layer and application to large substrates canbe easily made. Thus, the display device of this embodiment can bemanufactured with high mass productivity at low cost.

In Example 1 of manufacturing method of display device, the electrode ofthe display element can be formed by processing the separation layerthat is exposed by peeling. Since the electrode is formed using theseparation layer, the removal of the separation layer is not required.In addition, a conductive film to be the electrode of the displayelement does not need to be formed in a different step than theseparation layer. Accordingly, a manufacturing process can besimplified.

Example 2 of Manufacturing Method of Display Device

Next, a manufacturing method of a display device that is different fromthat described in Example 1 of manufacturing method of display devicewill be specifically described.

Example 2 of manufacturing method of display device is different fromExample 1 of manufacturing method of display device mainly in that thereflective electrode of the liquid crystal element is formed withoutusing the separation layer 311 and in that the separation layer 311 isremoved after peeling.

Note that detailed descriptions of steps similar to those in Example 1of manufacturing method of display device are sometimes omitted.

First, components from the coloring layer 131 to the alignment film 133b are formed over the substrate 361 (FIG. 9A). Steps for forming thecomponents are similar to those described with reference to FIG. 5A inExample 1 of manufacturing method of display device.

Note that steps illustrated in FIGS. 9B, 9C1, and 9C2, FIGS. 10A and10B, FIGS. 11A and 11B, and FIGS. 12A and 12B are performedindependently of the steps illustrated in FIG. 9A.

First, the separation layer 311 is formed over the formation substrate350 (FIG. 9B). In the step illustrated in FIG. 9B, a material isselected that would cause separation at the interface between theformation substrate 350 and the separation layer 311 when the formationsubstrate 350 is peeled.

Alternatively, as described in Example 1 of manufacturing method ofdisplay device with reference to FIG. 5B2, the insulating layer 355 maybe formed over the formation substrate 350 and the separation layer 311may be formed over the insulating layer 355.

Since the reflective electrode of the liquid crystal element is formedwithout using the separation layer 311 in Example 2 of manufacturingmethod of display device, the separation layer 311 does not necessarilyhave reflexibility.

Then, an electrode 111 and a conductive layer 111 c are formed over theseparation layer 311 (FIG. 9C1). The electrode 111 has the opening 451above the separation layer 311. The electrode 111 and the conductivelayer 111 c can be formed in the following manner: a conductive film isformed, a resist mask is formed, the conductive film is etched, and theresist mask is removed. The electrode 111 and the conductive layer 111 care formed using a conductive material that reflects visible light.

Alternatively, an electrode 111 a and the conductive layer 111 c areformed over the separation layer 311, an electrode 111 b is formed overthe electrode 111 a, and a conductive layer 111 d is formed over theconductive layer 111 c (FIG. 9C2). The electrode 111 b has the opening451 above the electrode 111 a. The electrode 111 a and the conductivelayer 111 c can be formed in the following manner: a conductive film isformed, a resist mask is formed, the conductive film is etched, and theresist mask is removed. The electrode 111 b and the conductive layer 111d can be formed in a similar manner. The electrode 111 a and theconductive layer 111 c are formed using a conductive material thattransmits visible light. The electrode 111 b and the conductive layer111 d are formed using a conductive material that reflects visiblelight.

As illustrated in FIG. 9C2, the electrode 111 a that transmits visiblelight is preferably provided across the opening 451. Accordingly, liquidcrystals are aligned in a region overlapping with the opening 451 as inthe other regions, in which case an alignment defect of the liquidcrystals is prevented from being generated in a boundary portion ofthese regions and undesired light leakage can be suppressed.

As described above, the separation layer 311 is removed after thepeeling in Example 2 of manufacturing method of display device. Thus, itis preferable that the etching selectivity ratio of the separation layer311 to the electrode 111 (or the electrode 111 a) in contact with theseparation layer 311 be sufficiently large, in which case the electrode111 (or the electrode 111 a) can be prevented from being removed whenthe separation layer 311 is removed.

The following description is for the case of employing the stepillustrated in FIG. 9C1. Note that the following description can also beapplied to the case of employing the step illustrated in FIG. 9C2.

The insulating layer 220 is formed (FIG. 10A). Then, an opening thatreaches the electrode 111 is provided in the insulating layer 220.

Next, the connection portion 204, the connection portion 207, thetransistor 205, and the transistor 206 are formed over the insulatinglayer 220.

Specifically, first, the conductive layer 221 a, the conductive layer221 b, and the conductive layer 221 c are formed over the insulatinglayer 220. At this time, the conductive layer 221 b and the electrode111 are connected to each other through the opening in the insulatinglayer 220 at the connection portion 207, and the conductive layer 221 cand the conductive layer 111 c are connected to each other through theopening in the insulating layer 220 at the connection portion 204.

Subsequently, the insulating layer 211 is formed and the semiconductorlayer 231 is formed over the insulating layer 211.

Next, the conductive layers 222 a and 222 b and the wiring 365 areformed. Here, the conductive layer 222 a included in the transistor 206is electrically connected to the conductive layer 221 b. As a result,the electrode 111 and the conductive layer 222 a can be electricallyconnected to each other at the connection portion 207. At the connectionportion 204, the wiring 365 and the conductive layer 111 c areelectrically connected to each other with the conductive layer 221 cprovided therebetween.

In the above manner, the transistor 206 can be fabricated (FIG. 10A).

Next, the insulating layer 212 that covers the transistor 206 is formedand the conductive layer 223 is formed over the insulating layer 212, sothat the transistor 205 is completed (FIG. 10A).

Then, the insulating layer 213 is formed and the coloring layer 134 isformed over the insulating layer 213 (FIG. 10A). After that, componentsfrom the insulating layer 214 to the insulating layer 194 are formed(FIG. 10B). Next, the substrate 351 is bonded to a surface of theinsulating layer 194 with the adhesive layer 142 (FIG. 10B). Steps forforming the components are similar to those described with reference toFIG. 5C and FIGS. 6A to 6C in Example 1 of manufacturing method ofdisplay device.

After that, the formation substrate 350 is peeled (FIG. 11A).

The separation occurs at the interface between the separation layer 311and the formation substrate 350, so that the separation layer 311 isexposed (FIGS. 11A and 11B).

Next, the separation layer 311 is removed so that the insulating layer220, the conductive layer 111 c, and the electrode 111 are exposed (FIG.12A). The separation layer 311 can be removed by wet etching or dryetching. The use of the condition where the etching selectivity ratio ofthe separation layer 311 to the electrode 111 and the conductive layer111 c is large can prevent the electrode 111 and the conductive layer111 c from being removed.

In the case of using titanium for the separation layer 311, for example,an ammonia hydrogen peroxide mixture (a mixed solution of ammonia,water, and a hydrogen peroxide solution) is preferably used becauseetching can be performed at room temperature and the etching selectivityratio to other films can be large.

Subsequently, the alignment film 133 a is formed over the electrode 111(FIG. 12B). The alignment film 133 a can be formed in the followingmanner: a thin film is formed using a resin or the like, and then,rubbing treatment is performed.

Then, the substrate 361 obtained from the steps described using FIG. 9Aand the substrate 351 obtained from the steps up to the step illustratedin FIG. 12B are bonded to each other with the liquid crystal layer 112provided therebetween (FIG. 13A). The substrate 351 and the substrate361 are bonded to each other with the adhesive layer 141.

In the liquid crystal element 180 illustrated in FIG. 13A, the electrode111 part of which functions as the pixel electrode, the liquid crystallayer 112, and the electrode 113 part of which functions as the commonelectrode are stacked. The liquid crystal element 180 is formed so as tooverlap with the coloring layer 131.

The polarizing plate 135 is placed on the outer surface of the substrate361. Furthermore, the FPC 372 and the wiring 365 are electricallyconnected to each other through the connection layer 242.

FIG. 13B is a cross-sectional view of a display device, which is formedin the case of employing the step illustrated in FIG. 9C2. The displaydevice illustrated in FIG. 13B does not include the electrode 111 butthe electrode 111 a and the electrode 111 b.

As described above, in Example 2 of manufacturing method of displaydevice, the surface of the separation layer does not particularly needto be subjected to treatment such as plasma treatment after theformation of the separation layer. Furthermore, a low-cost material canbe used for the separation layer and application to large substrates canbe easily made. Thus, the display device of this embodiment can bemanufactured with high mass productivity at low cost.

Structure Example of Transistor

There is no particular limitation on the structure of the transistorincluded in the display device of one embodiment of the presentinvention. For example, a planar transistor, a staggered transistor, oran inverted staggered transistor may be used. A top-gate transistor or abottom-gate transistor may be used. Gate electrodes may be providedabove and below a channel.

FIGS. 14A to 14E illustrate structure examples of transistors.

A transistor 110 a illustrated in FIG. 14A is a top-gate transistor.

The transistor 110 a includes a conductive layer 221, the insulatinglayer 211, the semiconductor layer 231, the insulating layer 212, theconductive layer 222 a, and the conductive layer 222 b. Thesemiconductor layer 231 is provided over an insulating layer 151. Theconductive layer 221 overlaps with the semiconductor layer 231 with theinsulating layer 211 positioned therebetween. The conductive layer 222 aand the conductive layer 222 b are electrically connected to thesemiconductor layer 231 through openings provided in the insulatinglayer 211 and the insulating layer 212.

The conductive layer 221 functions as a gate. The insulating layer 211functions as a gate insulating layer. One of the conductive layer 222 aand the conductive layer 222 b functions as a source and the otherfunctions as a drain.

In the transistor 110 a, the conductive layer 221 can be physicallydistanced from the conductive layer 222 a or 222 b easily; thus, theparasitic capacitance between the conductive layer 221 and theconductive layer 222 a or 222 b can be reduced.

A transistor 110 b illustrated in FIG. 14B includes, in addition to thecomponents of the transistor 110 a, the conductive layer 223 and aninsulating layer 218. The conductive layer 223 is provided over theinsulating layer 151. The conductive layer 223 overlaps with thesemiconductor layer 231. The insulating layer 218 covers the conductivelayer 223 and the insulating layer 151.

The conductive layer 223 functions as one of a pair of gates. Thus, theon-state current of the transistor can be increased and the thresholdvoltage can be controlled.

FIGS. 14C to 14E each illustrate an example of a stacked-layer structureof two transistors. The structures of the two stacked transistors can beindependently determined, and the combination of the structures is notlimited to those illustrated in FIGS. 14C to 14E.

FIG. 14C illustrates a stacked-layer structure of a transistor 110 c anda transistor 110 d. The transistor 110 c includes two gates. Thetransistor 110 d has a bottom-gate structure. Note that the transistor110 c may have a structure including one gate (top-gate structure). Thetransistor 110 d may include two gates.

The transistor 110 c includes the conductive layer 223, the insulatinglayer 218, the semiconductor layer 231, the conductive layer 221, theinsulating layer 211, the conductive layer 222 a, and the conductivelayer 222 b. The conductive layer 223 is provided over the insulatinglayer 151. The conductive layer 223 overlaps with the semiconductorlayer 231 with the insulating layer 218 positioned therebetween. Theinsulating layer 218 covers the conductive layer 223 and the insulatinglayer 151. The conductive layer 221 overlaps with the semiconductorlayer 231 with the insulating layer 211 positioned therebetween.Although FIG. 14C illustrates an example where the insulating layer 211is provided only in a region overlapping with the conductive layer 221,the insulating layer 211 may be provided so as to cover an end portionof the semiconductor layer 231, as illustrated in FIG. 14B and otherdrawings. The conductive layer 222 a and the conductive layer 222 b areelectrically connected to the semiconductor layer 231 through openingsprovided in the insulating layer 212.

The transistor 110 d includes the conductive layer 222 b, the insulatinglayer 213, the semiconductor layer 261, the conductive layer 263 a, andthe conductive layer 263 b. The conductive layer 222 b includes a regionoverlapping with the semiconductor layer 261 with the insulating layer213 positioned therebetween. The insulating layer 213 covers theconductive layer 222 b. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261.

The conductive layer 221 and the conductive layer 223 each function as agate of the transistor 110 c. The insulating layer 218 and theinsulating layer 211 each function as a gate insulating layer of thetransistor 110 c. The conductive layer 222 a functions as one of asource and a drain of the transistor 110 c.

The conductive layer 222 b has a portion functioning as the other of thesource and the drain of the transistor 110 c and a portion functioningas a gate of the transistor 110 d. The insulating layer 213 functions asa gate insulating layer of the transistor 110 d. One of the conductivelayer 263 a and the conductive layer 263 b functions as a source of thetransistor 110 d and the other functions as a drain of the transistor110 d.

The transistor 110 c and the transistor 110 d are preferably applied toa pixel circuit of the light-emitting element 170. For example, thetransistor 110 c can be used as a selection transistor and thetransistor 110 d can be used as a driving transistor.

The conductive layer 263 b is electrically connected to the electrode191 that functions as a pixel electrode of the light-emitting elementthrough an opening provided in the insulating layer 217 and theinsulating layer 214.

FIG. 14D illustrates a stacked-layer structure of a transistor 110 e anda transistor 110 f. The transistor 110 e has a bottom-gate structure.The transistor 110 f includes two gates. The transistor 110 e mayinclude two gates.

The transistor 110 e includes the conductive layer 221, the insulatinglayer 211, the semiconductor layer 231, the conductive layer 222 a, andthe conductive layer 222 b. The conductive layer 221 is provided overthe insulating layer 151. The conductive layer 221 overlaps with thesemiconductor layer 231 with the insulating layer 211 positionedtherebetween. The insulating layer 211 covers the conductive layer 221and the insulating layer 151. The conductive layer 222 a and theconductive layer 222 b are electrically connected to the semiconductorlayer 231.

The transistor 110 f includes the conductive layer 222 b, the insulatinglayer 212, the semiconductor layer 261, the conductive layer 223, theinsulating layer 218, the insulating layer 213, the conductive layer 263a, and the conductive layer 263 b. The conductive layer 222 b includes aregion overlapping with the semiconductor layer 261 with the insulatinglayer 212 positioned therebetween. The insulating layer 212 covers theconductive layer 222 b. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261through openings provided in the insulating layer 213. The conductivelayer 223 overlaps with the semiconductor layer 261 with the insulatinglayer 218 positioned therebetween. The insulating layer 218 is providedin a region overlapping with the conductive layer 223.

The conductive layer 221 functions as a gate of the transistor 110 e.The insulating layer 211 functions as a gate insulating layer of thetransistor 110 e. The conductive layer 222 a functions as one of asource and a drain of the transistor 110 e.

The conductive layer 222 b has a portion functioning as the other of thesource and the drain of the transistor 110 e and a portion functioningas a gate of the transistor 110 f. The conductive layer 223 functions asanother gate of the transistor 110 f. The insulating layer 212 and theinsulating layer 218 each function as a gate insulating layer of thetransistor 110 f. One of the conductive layer 263 a and the conductivelayer 263 b functions as a source of the transistor 110 f and the otherfunctions as a drain of the transistor 110 f.

The conductive layer 263 b is electrically connected to the electrode191 that functions as a pixel electrode of a light-emitting elementthrough an opening provided in the insulating layer 214.

FIG. 14E illustrates a stacked-layer structure of a transistor 110 g anda transistor 110 h. The transistor 110 g has a top-gate structure. Thetransistor 110 h includes two gates. The transistor 110 g may includetwo gates.

The transistor 110 g includes the semiconductor layer 231, theconductive layer 221, the insulating layer 211, the conductive layer 222a, and the conductive layer 222 b. The semiconductor layer 231 isprovided over the insulating layer 151. The conductive layer 221overlaps with the semiconductor layer 231 with the insulating layer 211positioned therebetween. The insulating layer 211 overlaps with theconductive layer 221. The conductive layer 222 a and the conductivelayer 222 b are electrically connected to the semiconductor layer 231through openings provided in the insulating layer 212.

The transistor 110 h includes the conductive layer 222 b, the insulatinglayer 213, the semiconductor layer 261, the conductive layer 223, theinsulating layer 218, the insulating layer 217, the conductive layer 263a, and the conductive layer 263 b. The conductive layer 222 b includes aregion overlapping with the semiconductor layer 261 with the insulatinglayer 213 positioned therebetween. The insulating layer 213 covers theconductive layer 222 b. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261through openings provided in the insulating layer 217. The conductivelayer 223 overlaps with the semiconductor layer 261 with the insulatinglayer 218 positioned therebetween. The insulating layer 218 is providedin a region overlapping with the conductive layer 223.

The conductive layer 221 functions as a gate of the transistor 110 g.The insulating layer 211 functions as a gate insulating layer of thetransistor 110 g. The conductive layer 222 a functions as one of asource and a drain of the transistor 110 g.

The conductive layer 222 b has a portion functioning as the other of thesource and the drain of the transistor 110 g and a portion functioningas a gate of the transistor 110 h. The conductive layer 223 functions asanother gate of the transistor 110 h. The insulating layer 213 and theinsulating layer 218 each function as a gate insulating layer of thetransistor 110 h. One of the conductive layer 263 a and the conductivelayer 263 b functions as a source of the transistor 110 h and the otherfunctions as a drain of the transistor 110 h.

The conductive layer 263 b is electrically connected to the electrode191 that functions as a pixel electrode of a light-emitting elementthrough an opening provided in the insulating layer 214.

The display device of this embodiment includes two types of displayelements as described above; thus, switching between a plurality ofdisplay modes is possible. Accordingly, the display device can have highvisibility regardless of the ambient brightness, leading to highconvenience.

In any of the manufacturing methods of a display device of thisembodiment, the surface of the separation layer does not particularlyneed to be subjected to treatment such as plasma treatment after theformation of the separation layer. Furthermore, a low-cost material canbe used for the separation layer and application to large substrates canbe easily made. Thus, the display device of this embodiment can bemanufactured with high mass productivity at low cost.

Furthermore, since the electrode of the display element can be formedusing the separation layer, the removal of the separation layer is notrequired. In addition, the electrode of the display element does notneed to be formed in a different step than the separation layer.Accordingly, a manufacturing process can be simplified.

This embodiment can be combined with any other embodiment asappropriate. In the case where a plurality of structure examples aredescribed in one embodiment in this specification, some of the structureexamples can be combined as appropriate.

Embodiment 2

In this embodiment, more specific structure examples of the displaydevice described in Embodiment 1 will be described with reference toFIGS. 15A, 15B1, 15B2, 15B3, and 15B4, FIG. 16, and FIGS. 17A and 17B.

FIG. 15A is a block diagram of a display device 400. The display device400 includes the display portion 362, a circuit GD, and a circuit SD.The display portion 362 includes a plurality of pixels 410 arranged in amatrix.

The display device 400 includes a plurality of wirings G1, a pluralityof wirings G2, a plurality of wirings ANO, a plurality of wirings CSCOM,a plurality of wirings S1, and a plurality of wirings S2. The pluralityof wirings G1, the plurality of wirings G2, the plurality of wiringsANO, and the plurality of wirings CSCOM are each electrically connectedto the circuit GD and the plurality of pixels 410 arranged in adirection indicated by an arrow R. The plurality of wirings S1 and theplurality of wirings S2 are each electrically connected to the circuitSD and the plurality of pixels 410 arranged in a direction indicated byan arrow C.

Although the structure including one circuit GD and one circuit SD isillustrated here for simplicity, the circuit GD and the circuit SD fordriving liquid crystal elements and the circuit GD and the circuit SDfor driving light-emitting elements may be provided separately.

The pixels 410 each include a reflective liquid crystal element and alight-emitting element.

FIGS. 15B1, 15B2, 15B3, and 15B4 illustrate structure examples of theelectrode 311 a included in the pixel 410. The electrode 311 a serves asa reflective electrode of the liquid crystal element. The opening 451 isprovided in the electrode 311 a in FIGS. 15B1 and 15B2.

In FIGS. 15B1 and 15B2, a light-emitting element 360 positioned in aregion overlapping with the electrode 311 a is indicated by a brokenline. The light-emitting element 360 overlaps with the opening 451included in the electrode 311 a. Thus, light from the light-emittingelement 360 is emitted to the display surface side through the opening451.

In FIG. 15B1, the pixels 410 which are adjacent in the directionindicated by the arrow R are pixels emitting light of different colors.As illustrated in FIG. 15B1, the openings 451 are preferably provided indifferent positions in the electrodes 311 a so as not to be aligned intwo adjacent pixels provided in the direction indicated by the arrow R.This allows two light-emitting elements 360 to be apart from each other,thereby preventing light emitted from the light-emitting element 360from entering a coloring layer in the adjacent pixel 410 (such aphenomenon is referred to as crosstalk). Furthermore, since two adjacentlight-emitting elements 360 can be arranged apart from each other, ahigh-resolution display device is achieved even when EL layers of thelight-emitting elements 360 are separately formed with a blocking maskor the like.

In FIG. 15B2, the pixels 410 which are adjacent in a direction indicatedby the arrow C are pixels emitting light of different colors. Also inFIG. 15B2, the openings 451 are preferably provided in differentpositions in the electrodes 311 a so as not to be aligned in twoadjacent pixels provided in the direction indicated by the arrow C.

The smaller the ratio of the total area of the opening 451 to the totalarea except for the opening is, the brighter an image displayed usingthe liquid crystal element can be. Furthermore, the larger the ratio ofthe total area of the opening 451 to the total area except for theopening is, the brighter an image displayed using the light-emittingelement 360 can be.

The opening 451 may have a polygonal shape, a quadrangular shape, anelliptical shape, a circular shape, a cross-like shape, a stripe shape,a slit-like shape, or a checkered pattern, for example. The opening 451may be provided close to the adjacent pixel. Preferably, the opening 451is provided close to another pixel emitting light of the same color, inwhich case crosstalk can be suppressed.

As illustrated in FIGS. 15B3 and 15B4, a light-emitting region of thelight-emitting element 360 may be positioned in a region where theelectrode 311 a is not provided, in which case light emitted from thelight-emitting element 360 is emitted to the display surface side.

In FIG. 15B3, the light-emitting elements 360 are not aligned in twoadjacent pixels 410 provided in the direction indicated by the arrow R.In FIG. 15B4, the light-emitting elements 360 are aligned in twoadjacent pixels 410 provided in the direction indicated by the arrow R.

The structure illustrated in FIG. 15B3 can, as mentioned above, preventcrosstalk and increase the resolution because the light-emittingelements 360 included in two adjacent pixels 410 can be apart from eachother. The structure illustrated in FIG. 15B4 can prevent light emittedfrom the light-emitting element 360 from being blocked by the electrode311 a because the electrode 311 a is not positioned along a side of thelight-emitting element 360 which is parallel to the direction indicatedby the arrow C. Thus, high viewing angle characteristics can beachieved.

As the circuit GD, any of a variety of sequential circuits such as ashift register can be used. In the circuit GD, a transistor, acapacitor, and the like can be used. A transistor included in thecircuit GD can be formed in the same steps as the transistors includedin the pixels 410.

The circuit SD is electrically connected to the wirings 51. For example,an integrated circuit can be used as the circuit SD. Specifically, anintegrated circuit formed on a silicon substrate can be used as thecircuit SD.

For example, a COG method, a COF method, or the like can be used tomount the circuit SD on a pad electrically connected to the pixels 410.Specifically, an anisotropic conductive film can be used to mount anintegrated circuit on the pad.

FIG. 16 is an example of a circuit diagram of the pixels 410. FIG. 16illustrates two adjacent pixels 410.

The pixels 410 each include a switch SW1, a capacitor C1, a liquidcrystal element 340, a switch SW2, a transistor M, a capacitor C2, thelight-emitting element 360, and the like. The pixel 410 is electricallyconnected to the wiring G1, the wiring G2, the wiring ANO, the wiringCSCOM, the wiring S1, and the wiring S2. FIG. 16 illustrates a wiringVCOM1 electrically connected to the liquid crystal element 340 and awiring VCOM2 electrically connected to the light-emitting element 360.

FIG. 16 illustrates an example in which a transistor is used as each ofthe switches SW1 and SW2.

A gate of the switch SW1 is connected to the wiring G1. One of a sourceand a drain of the switch SW1 is connected to the wiring S1, and theother is connected to one electrode of the capacitor C1 and oneelectrode of the liquid crystal element 340. The other electrode of thecapacitor C1 is connected to the wiring CSCOM. The other electrode ofthe liquid crystal element 340 is connected to the wiring VCOM1.

A gate of the switch SW2 is connected to the wiring G2. One of a sourceand a drain of the switch SW2 is connected to the wiring S2, and theother is connected to one electrode of the capacitor C2 and gates of thetransistor M. The other electrode of the capacitor C2 is connected toone of a source and a drain of the transistor M and the wiring ANO. Theother of the source and the drain of the transistor M is connected toone electrode of the light-emitting element 360. Furthermore, the otherelectrode of the light-emitting element 360 is connected to the wiringVCOM2.

FIG. 16 illustrates an example where the transistor M includes two gatesbetween which a semiconductor is provided and which are connected toeach other. This structure can increase the amount of current flowing inthe transistor M.

The wiring G1 can be supplied with a signal for changing the on/offstate of the switch SW1. A predetermined potential can be supplied tothe wiring VCOM1. The wiring S1 can be supplied with a signal forchanging the orientation of liquid crystals of the liquid crystalelement 340. A predetermined potential can be supplied to the wiringCSCOM.

The wiring G2 can be supplied with a signal for changing the on/offstate of the switch SW2. The wiring VCOM2 and the wiring ANO can besupplied with potentials having a difference large enough to make thelight-emitting element 360 emit light. The wiring S2 can be suppliedwith a signal for changing the conduction state of the transistor M.

In the pixel 410 of FIG. 16, for example, an image can be displayed inthe reflective mode by driving the pixel with the signals supplied tothe wiring G1 and the wiring S1 and utilizing the optical modulation ofthe liquid crystal element 340. In the case where an image is displayedin the transmissive mode, the pixel is driven with the signals suppliedto the wiring G2 and the wiring S2 and the light-emitting element 360emits light. In the case where both modes are performed at the sametime, the pixel can be driven with the signals supplied to the wiringG1, the wiring G2, the wiring S1, and the wiring S2.

Although FIG. 16 illustrates an example in which one liquid crystalelement 340 and one light-emitting element 360 are provided in one pixel410, one embodiment of the present invention is not limited thereto.FIG. 17A illustrates an example in which one liquid crystal element 340and four light-emitting elements 360 (light-emitting elements 360 r, 360g, 360 b, and 360 w) are provided in one pixel 410. The pixel 410illustrated in FIG. 17A differs from that in FIG. 16 in being capable ofdisplaying a full-color image with the use of the light-emittingelements by one pixel.

In FIG. 17A, in addition to the wirings in FIG. 16, a wiring G3 and awiring S3 are connected to the pixel 410.

In the example in FIG. 17A, light-emitting elements emitting red light(R), green light (G), blue light (B), and white light (W) can be used asthe four light-emitting elements 360, for example. Furthermore, as theliquid crystal element 340, a reflective liquid crystal element emittingwhite light can be used. Thus, in the case of displaying an image in thereflective mode, a white image can be displayed with high reflectivity.In the case of displaying an image in the transmissive mode, an imagecan be displayed with a higher color rendering property at low powerconsumption.

FIG. 17B illustrates a structure example of the pixel 410 correspondingto FIG. 17A. The pixel 410 includes the light-emitting element 360 woverlapping with the opening included in the electrode 311 a and thelight-emitting element 360 r, the light-emitting element 360 g, and thelight-emitting element 360 b which are arranged in the periphery of theelectrode 311 a. It is preferable that the light-emitting elements 360r, 360 g, and 360 b have almost the same light-emitting area.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 3

In this embodiment, described below is the composition of acloud-aligned composite oxide semiconductor (CAC-OS) applicable to atransistor disclosed in one embodiment of the present invention.

The CAC-OS has, for example, a composition in which elements included inan oxide semiconductor are unevenly distributed. Materials includingunevenly distributed elements each have a size of greater than or equalto 0.5 nm and less than or equal to 10 nm, preferably greater than orequal to 1 nm and less than or equal to 2 nm, or a similar size. Notethat in the following description of an oxide semiconductor, a state inwhich one or more metal elements are unevenly distributed and regionsincluding the metal element(s) are mixed is referred to as a mosaicpattern or a patch-like pattern. The region has a size of greater thanor equal to 0.5 nm and less than or equal to 10 nm, preferably greaterthan or equal to 1 nm and less than or equal to 2 nm, or a similar size.

Note that an oxide semiconductor preferably contains at least indium. Inparticular, indium and zinc are preferably contained. In addition, oneor more of, aluminum, gallium, yttrium, copper, vanadium, beryllium,boron, silicon, titanium, iron, nickel, germanium, zirconium,molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten,magnesium, and the like may be contained.

For example, of the CAC-OS, an In—Ga—Zn oxide with the CAC composition(such an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO) hasa composition in which materials are separated into indium oxide(InO_(X1), where X1 is a real number greater than 0) or indium zincoxide (In_(X2)Zn_(Y2)O_(Z2), where X2, Y2, and Z2 are real numbersgreater than 0), and gallium oxide (GaO_(X3), where X3 is a real numbergreater than 0) or gallium zinc oxide (Ga_(X4)Zn_(Y4)O_(Z4), where X4,Y4, and Z4 are real numbers greater than 0), and a mosaic pattern isformed. Then, InO_(X1) or In_(X2)Zn_(Y2)O_(Z2) forming the mosaicpattern is evenly distributed in the film. This composition is alsoreferred to as a cloud-like composition.

That is, the CAC-OS is a composite oxide semiconductor with acomposition in which a region including GaO_(X3) as a main component anda region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main componentare mixed. Note that in this specification, for example, when the atomicratio of In to an element M in a first region is greater than the atomicratio of In to an element M in a second region, the first region isdescribed as having higher In concentration than the second region.

Note that a compound including In, Ga, Zn, and O is also known as IGZO.Typical examples of IGZO include a crystalline compound represented byInGaO₃(ZnO)_(m1) (m1 is a natural number) and a crystalline compoundrepresented by In_((1+x0))Ga_((1−x0))O₃(ZnO)_(m0) (−1≦x0≦1; m0 is agiven number).

The above crystalline compounds have a single crystal structure, apolycrystalline structure, or a CAAC structure. Note that the CAACstructure is a crystal structure in which a plurality of IGZOnanocrystals have c-axis alignment and are connected in the a-b planedirection without alignment.

The CAC-OS relates to the material composition of an oxidesemiconductor. In a material composition of a CAC-OS including In, Ga,Zn, and O, nanoparticle regions including Ga as a main component areobserved in part of the CAC-OS and nanoparticle regions including In asa main component are observed in part thereof. These nanoparticleregions are randomly dispersed to form a mosaic pattern. Therefore, thecrystal structure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a stacked-layer structure of two or more filmswith different atomic ratios is not included. For example, a two-layerstructure of a film including In as a main component and a filmincluding Ga as a main component is not included.

A boundary between the region including GaO_(X3) as a main component andthe region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent is not clearly observed in some cases.

In the case where one or more of aluminum, yttrium, copper, vanadium,beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium,molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten,magnesium, and the like are contained instead of gallium in a CAC-OS,nanoparticle regions including the selected metal element(s) as a maincomponent(s) are observed in part of the CAC-OS and nanoparticle regionsincluding In as a main component are observed in part thereof, and thesenanoparticle regions are randomly dispersed to form a mosaic pattern inthe CAC-OS.

The CAC-OS can be formed by a sputtering method under a condition wherea substrate is not heated intentionally. In the case where the CAC-OS isformed by a sputtering method, one or more of an inert gas (typically,argon), an oxygen gas, and a nitrogen gas can be used as a depositiongas. Furthermore, the flow rate of the oxygen gas to the total flow rateof the deposition gas in deposition is preferably as low as possible,for example, the flow rate of the oxygen gas is higher than or equal to0% and lower than 30%, preferably higher than or equal to 0% and lowerthan or equal to 10%.

The CAC-OS is characterized in that a clear peak is not observed whenmeasurement is conducted using a θ/2θ scan by an out-of-plane methodwith an X-ray diffraction (XRD). That is, it is found by the XRD thatthere are no alignment in the a-b plane direction and no alignment inthe c-axis direction in the measured areas.

In the CAC-OS, an electron diffraction pattern that is obtained byirradiation with an electron beam with a probe diameter of 1 nm (alsoreferred to as nanobeam electron beam) has regions with high luminancein a ring pattern and a plurality of bright spots appear in thering-like pattern. Thus, it is found from the electron diffractionpattern that the crystal structure of the CAC-OS includes ananocrystalline (nc) structure that does not show alignment in the planedirection and the cross-sectional direction.

For example, energy dispersive X-ray spectroscopy (EDX) is used toobtain EDX mapping, and according to the EDX mapping, the CAC-OS of theIn—Ga—Zn oxide has a composition in which the regions including GaOx3 asa main component and the regions including In_(X2)Zn_(Y2)O_(Z2) orInO_(X1) as a main component are unevenly distributed and mixed.

The CAC-OS has a structure different from that of an IGZO compound inwhich metal elements are evenly distributed, and has characteristicsdifferent from those of the IGZO compound. That is, in the CAC-OS,regions including GaO_(X3) or the like as a main component and regionsincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component areseparated to form a mosaic pattern.

The conductivity of a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)as a main component is higher than that of a region including GaO_(X3)or the like as a main component. In other words, when carriers flowthrough regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent, the conductivity of an oxide semiconductor is exhibited.Accordingly, when regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) asa main component are distributed in an oxide semiconductor like a cloud,high field-effect mobility (μ) can be achieved.

In contrast, the insulating property of a region including GaO_(X3) orthe like as a main component is higher than that of a region includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. In other words,when regions including GaO_(X3) or the like as a main component aredistributed in an oxide semiconductor, leakage current can be suppressedand favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor element, theinsulating property derived from GaO_(X3) or the like and theconductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) complementeach other, whereby high on-state current (I_(on)) and high field-effectmobility (μ) can be achieved.

A semiconductor element including a CAC-OS has high reliability. Thus,the CAC-OS is suitably used in a variety of semiconductor devicestypified by a display.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 4

In this embodiment, a display module and electronic devices ofembodiments of the present invention are described.

In a display module 8000 in FIG. 18, a touch panel 8004 connected to anFPC 8003, a display panel 8006 connected to an FPC 8005, a frame 8009, aprinted circuit board 8010, and a battery 8011 are provided between anupper cover 8001 and a lower cover 8002.

The display device of one embodiment of the present invention can beused for, for example, the display panel 8006. In that case, a displaymodule with high visibility regardless of the ambient brightness or adisplay module with low power consumption can be fabricated.

The shape and size of the upper cover 8001 and the lower cover 8002 canbe changed as appropriate depending on the sizes of the touch panel 8004and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and can be formed to overlap with the display panel 8006.Instead of providing the touch panel 8004, the display panel 8006 canhave a touch panel function.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed circuit board 8010. The frame 8009 can alsofunction as a radiator plate.

The printed circuit board 8010 includes a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying power to the power supplycircuit, an external commercial power source or the battery 8011provided separately may be used. The battery 8011 can be omitted in thecase of using a commercial power source.

The display module 8000 may be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

The display device of one embodiment of the present invention canachieve high visibility regardless of the intensity of external light.Thus, the display device of one embodiment of the present invention canbe suitably used for a portable electronic device, a wearable electronicdevice (wearable device), an e-book reader, or the like.

A portable information terminal 800 illustrated in FIGS. 19A and 19Bincludes a housing 801, a housing 802, a display portion 803, a displayportion 804, a hinge portion 805, and the like.

The housing 801 and the housing 802 are joined together with the hingeportion 805. The portable information terminal 800 can be opened asillustrated in FIG. 19B from a closed state (FIG. 19A).

The display device of one embodiment of the present invention can beused for at least one of the display portion 803 and the display portion804. In that case, a portable information terminal with high visibilityregardless of the ambient brightness or a portable information terminalwith low power consumption can be fabricated.

The display portion 803 and the display portion 804 can each display atleast one of a text, a still image, a moving image, and the like. When atext is displayed on the display portion, the portable informationterminal 800 can be used as an e-book reader.

Since the portable information terminal 800 is foldable, the portableinformation terminal 800 has high portability and excellent versatility.

A power button, an operation button, an external connection port, aspeaker, a microphone, or the like may be provided for the housing 801and the housing 802.

A portable information terminal 810 illustrated in FIG. 19C includes ahousing 811, a display portion 812, an operation button 813, an externalconnection port 814, a speaker 815, a microphone 816, a camera 817, andthe like.

The display device of one embodiment of the present invention can beused for the display portion 812. In that case, a portable informationterminal with high visibility regardless of the ambient brightness or aportable information terminal with low power consumption can befabricated.

The portable information terminal 810 includes a touch sensor in thedisplay portion 812. Operations such as making a call and inputting acharacter can be performed by touch on the display portion 812 with afinger, a stylus, or the like.

With the operation button 813, the power can be turned on or off. Inaddition, types of images displayed on the display portion 812 can beswitched; for example, switching an image from a mail creation screen toa main menu screen is performed with the operation button 813.

When a detection device such as a gyroscope sensor or an accelerationsensor is provided inside the portable information terminal 810, thedirection of display on the screen of the display portion 812 can beautomatically changed by determining the orientation of the portableinformation terminal 810 (whether the portable information terminal 810is placed horizontally or vertically). Furthermore, the direction ofdisplay on the screen can be changed by touch on the display portion812, operation with the operation button 813, sound input using themicrophone 816, or the like.

The portable information terminal 810 functions as, for example, one ormore of a telephone set, a notebook, and an information browsing system.Specifically, the portable information terminal 810 can be used as asmartphone. The portable information terminal 810 is capable ofexecuting a variety of applications such as mobile phone calls,e-mailing, viewing and editing texts, music reproduction, reproducing amoving image, Internet communication, and computer games, for example.

A camera 820 illustrated in FIG. 19D includes a housing 821, a displayportion 822, operation buttons 823, a shutter button 824, and the like.Furthermore, an attachable lens 826 is attached to the camera 820.

The display device of one embodiment of the present invention can beused for the display portion 822. The use of the display portion withhigh visibility regardless of the ambient brightness can increase theconvenience of the camera. Furthermore, a camera with low powerconsumption can be fabricated.

Although the lens 826 of the camera 820 here is detachable from thehousing 821 for replacement, the lens 826 may be incorporated into thehousing 821.

A still image or a moving image can be taken with the camera 820 at thepress of the shutter button 824. In addition, images can also be takenby the touch of the display portion 822 which serves as a touch panel.

Note that a stroboscope, a viewfinder, or the like can be additionallyattached to the camera 820. Alternatively, these may be incorporatedinto the housing 821.

FIGS. 20A to 20E illustrate electronic devices. These electronic deviceseach include a housing 9000, a display portion 9001, a speaker 9003, anoperation key 9005 (including a power switch or an operation switch), aconnection terminal 9006, a sensor 9007 (a sensor having a function ofmeasuring force, displacement, position, speed, acceleration, angularvelocity, rotational frequency, distance, light, liquid, magnetism,temperature, chemical substance, sound, time, hardness, electric field,current, voltage, power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), a microphone 9008, and the like.

The display device of one embodiment of the present invention can besuitably used for the display portion 9001. Thus, an electronic deviceincluding a display portion with high visibility regardless of thesurrounding brightness can be manufactured. Furthermore, an electronicdevice with low power consumption can be fabricated.

The electronic devices illustrated in FIGS. 20A to 20E can have avariety of functions, for example, a function of displaying a variety ofinformation (a still image, a moving image, a text image, and the like)on the display portion, a touch panel function, a function of displayinga calendar, the date, the time, and the like, a function of controllingprocessing with a variety of software (programs), a wirelesscommunication function, a function of being connected to a variety ofcomputer networks with a wireless communication function, a function oftransmitting and receiving a variety of data with a wirelesscommunication function, a function of reading a program or data storedin a storage medium and displaying the program or data on the displayportion, and the like. Note that the functions of the electronic devicesillustrated in FIGS. 20A to 20E are not limited to the above, and theelectronic devices may have other functions.

FIG. 20A is a perspective view of a watch-type portable informationterminal 9200. FIG. 20B is a perspective view of a watch-type portableinformation terminal 9201.

The portable information terminal 9200 illustrated in FIG. 20A iscapable of executing a variety of applications such as mobile phonecalls, e-mailing, viewing and editing texts, music reproduction,Internet communication, and computer games. The display surface of thedisplay portion 9001 is bent, and an image can be displayed on the bentdisplay surface. The portable information terminal 9200 can employ nearfield communication conformable to a communication standard. In thatcase, for example, mutual communication between the portable informationterminal 9200 and a headset capable of wireless communication can beperformed, and thus hands-free calling is possible. The portableinformation terminal 9200 includes the connection terminal 9006, anddata can be directly transmitted to and received from anotherinformation terminal via a connector. Power charging through theconnection terminal 9006 is also possible. Note that the chargingoperation may be performed by wireless power feeding without using theconnection terminal 9006.

Unlike in the portable information terminal illustrated in FIG. 20A, thedisplay surface of the display portion 9001 is not curved in theportable information terminal 9201 illustrated in FIG. 20B. Furthermore,the external state of the display portion of the portable informationterminal 9201 is a non-rectangular shape (a circular shape in FIG. 20B).

FIGS. 20C to 20E are perspective views of a foldable portableinformation terminal 9202. FIG. 20C is a perspective view illustratingthe portable information terminal 9202 that is opened. FIG. 20D is aperspective view illustrating the portable information terminal 9202that is being opened or being folded. FIG. 20E is a perspective viewillustrating the portable information terminal 9202 that is folded.

The folded portable information terminal 9202 is highly portable, andthe opened portable information terminal 9202 is highly browsable due toa seamless large display region. The display portion 9001 of theportable information terminal 9202 is supported by three housings 9000joined together by hinges 9055. By folding the portable informationterminal 9202 at a connection portion between two housings 9000 with thehinges 9055, the portable information terminal 9202 can be reversiblychanged in shape from opened to folded. For example, the portableinformation terminal 9202 can be bent with a radius of curvature ofgreater than or equal to 1 mm and less than or equal to 150 mm.

This embodiment can be combined with any other embodiment asappropriate.

This application is based on Japanese Patent Application serial No.2016-140282 filed with Japan Patent Office on Jul. 15, 2016, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A display device comprising: a first displayelement; a second display element; and an insulating layer, wherein thefirst display element comprises a first pixel electrode configured toreflect visible light and a liquid crystal layer, wherein the seconddisplay element is configured to emit visible light, wherein the seconddisplay element comprises a second pixel electrode and a commonelectrode, wherein the first pixel electrode is on an opposite side ofthe insulating layer from the second pixel electrode, wherein the liquidcrystal layer is on an opposite side of the first pixel electrode fromthe insulating layer, wherein the common electrode is on an oppositeside of the second pixel electrode from the insulating layer, whereinthe liquid crystal layer comprises a first region overlapping with thefirst pixel electrode and a second region overlapping with the seconddisplay element, and wherein a thickness of the liquid crystal layer inthe first region is smaller than a thickness of the liquid crystal layerin the second region.
 2. The display device according to claim 1 furthercomprising: a first transistor; and a second transistor, wherein thefirst transistor is configured to control driving of the first displayelement, wherein the second transistor is configured to control drivingof the second display element, and wherein the insulating layercomprises a portion serving as a gate insulating layer of the firsttransistor and a portion serving as a gate insulating layer of thesecond transistor.
 3. The display device according to claim 1, whereinthe first pixel electrode comprises an opening portion, wherein thesecond display element comprises a region overlapping with the openingportion, and wherein the second display element is configured to emitvisible light toward the opening portion.
 4. A display devicecomprising: a first display element; a second display element; a firstinsulating layer; a second insulating layer; a first transistor; and asecond transistor, wherein the first transistor is configured to controldriving of the first display element, wherein the second transistor isconfigured to control driving of the second display element, wherein thefirst display element comprises a first pixel electrode configured toreflect visible light and a liquid crystal layer, wherein the seconddisplay element is configured to emit visible light, wherein the seconddisplay element comprises a second pixel electrode and a commonelectrode, wherein the first transistor and the second transistor arebetween the first insulating layer and the second insulating layer,wherein the first transistor is electrically connected to the firstpixel electrode through an opening in the first insulating layer,wherein the second transistor is electrically connected to the secondpixel electrode through an opening in the second insulating layer,wherein the liquid crystal layer is on an opposite side of the firstpixel electrode from the first insulating layer, wherein the commonelectrode is on an opposite side of the second pixel electrode from thesecond insulating layer, wherein the liquid crystal layer comprises afirst region overlapping with the first pixel electrode and a secondregion overlapping with the second display element, and wherein athickness of the liquid crystal layer in the first region is smallerthan a thickness of the liquid crystal layer in the second region. 5.The display device according to claim 4, wherein one or both of thefirst transistor and the second transistor comprises an oxidesemiconductor in a channel formation region.
 6. The display deviceaccording to claim 4, wherein the first pixel electrode comprises anopening portion, wherein the second display element comprises a regionoverlapping with the opening portion, and wherein the second displayelement is configured to emit visible light toward the opening portion.7. A display module comprising: the display device according to claim 4;and a circuit board.
 8. An electronic device comprising: the displaymodule according to claim 7; and at least one of an antenna, a battery,a housing, a camera, a speaker, a microphone, and an operation button.9. A method for manufacturing a display device comprising: forming afirst common electrode over a first substrate; forming a separationlayer configured to reflect visible light over a formation substrate;forming an insulating layer over the separation layer; forming a seconddisplay element comprising a second pixel electrode configured totransmit visible light, a light-emitting layer, and a second commonelectrode configured to reflect visible light over the insulating layer;bonding the formation substrate and a second substrate to each otherwith the second display element interposed between the formationsubstrate and the second substrate; separating the formation substrateand the separation layer from each other; forming a first pixelelectrode by processing the separation layer after the step ofseparating; and bonding the first substrate and the second substrate toeach other with an adhesive with a liquid crystal layer interposedbetween the first common electrode and the first pixel electrode,wherein a first display element comprises the first pixel electrodeconfigured to reflect visible light, the liquid crystal layer, and thefirst common electrode configured to transmit visible light.
 10. Themethod for manufacturing a display device, according to claim 9, whereinthe separation layer is processed into the first pixel electrode havingan opening in a region overlapping with the second display element. 11.The method for manufacturing a display device, according to claim 9,wherein the adhesive used for bonding the first substrate and the secondsubstrate comprises a conductive particle, wherein the separation layeris processed into the first pixel electrode and a conductive layer inthe step of forming the first pixel electrode, and wherein the firstcommon electrode and the conductive layer are electrically connected toeach other via the conductive particle in the step of bonding the firstsubstrate and the second substrate.
 12. The manufacturing method of adisplay device, according to claim 9, wherein a nickel film is formed asthe separation layer in contact with the formation substrate, andwherein a maximum temperature applied to the separation layer in aperiod from forming the separation layer until separating the formationsubstrate and the separation layer from each other is higher than 150°C. and lower than 450° C.
 13. The manufacturing method of a displaydevice, according to claim 9, wherein a first insulating layercomprising nitrogen and silicon is formed over the formation substrate,wherein a second insulating layer comprising oxygen and silicon isformed over the first insulating layer, wherein a third insulating layercomprising oxygen, fluorine, and silicon is formed over the secondinsulating layer, and wherein a titanium film is formed as theseparation layer over the third insulating layer.
 14. A method formanufacturing a display device comprising: forming a first commonelectrode over a first substrate; forming a separation layer over aformation substrate; forming a first pixel electrode over the separationlayer; forming an insulating layer over the first pixel electrode;forming a second display element comprising a second pixel electrodeconfigured to transmit visible light, a light-emitting layer, and asecond common electrode configured to reflect visible light over theinsulating layer; bonding the formation substrate and a second substrateto each other with the second display element interposed between theformation substrate and the second substrate; separating the formationsubstrate and the separation layer from each other; removing theseparation layer to expose the first pixel electrode after the step ofseparating; and bonding the first substrate and the second substrate toeach other with an adhesive with a liquid crystal layer interposedbetween the first common electrode and the first pixel electrode,wherein a first display element comprises the first pixel electrodeconfigured to reflect visible light, the liquid crystal layer, and thefirst common electrode configured to transmit visible light.
 15. Themethod for manufacturing a display device according to claim 14, furthercomprising the steps of: providing an opening in the first pixelelectrode after the first pixel electrode is formed; and forming thesecond display element in a region overlapping with the opening.
 16. Themanufacturing method of a display device, according to claim 14, whereinthe adhesive used for bonding the first substrate and the secondsubstrate comprises a conductive particle, wherein the first pixelelectrode and a conductive layer are formed by processing a conductivefilm in the step of forming the first pixel electrode, and wherein thefirst common electrode and the conductive layer are electricallyconnected to each other via the conductive particle in the step ofbonding the first substrate and the second substrate.
 17. Themanufacturing method of a display device, according to claim 14, whereina nickel film is formed as the separation layer in contact with theformation substrate, and wherein a maximum temperature applied to theseparation layer in a period from forming the separation layer untilseparating the formation substrate and the separation layer from eachother is higher than 150° C. and lower than 450° C.
 18. Themanufacturing method of a display device, according to claim 14, whereina first insulating layer comprising nitrogen and silicon is formed overthe formation substrate, wherein a second insulating layer comprisingoxygen and silicon is formed over the first insulating layer, wherein athird insulating layer comprising oxygen, fluorine, and silicon isformed over the second insulating layer, and wherein a titanium film isformed as the separation layer over the third insulating layer.